THE    MODERN 


ASPHALT  PAVEMENT 


BY 

CLIFFORD    RICHARDSON 
ft 

M.  AM.  Soc.  C.  E.;    PROPRIETOR  NEW  YORK  TESTING   LABORATORY 


SECOND   EDITION,  REVISED    AND   ENLARGED 
THIRD  THOUSAND 


NEW  YORK 

JOHN   WILEY   &  SONS 

LONDON     CHAPMAN  &  HALL,  LIMITED 

1912 


V  r 

Copyright,  1905,  1908 


BY 

CLIFFORD  RICHARDSON 


THE  SCIENTIFIC 
ROBERT   DRUMMONO   AND   COMPANY 
BROOKLYN,   N.    Y. 


PREFACE  TO   FIRST  EDITION. 


THE  present  work  being  designed  for  a  rather  wide  class  of 
readers  necessarily  includes  a  large  collection  of  data  in  regard 
to  the  chemistry  of  asphalt  and  the  technology  of  the  industry, 
which  is  of  interest  only  to  civil  engineers,  asphalt  experts  and 
those  who  have  made  a  special  study  of  the  subject.  The  general 
reader  is  recommended  to  omit  Chapters  III  to  VIII,  XII,  and 
most  of  XVI,  or  to  confine  his  attention  to  the  resumes  of  them 
which  are  presented  at  the  end  of  each.  The  property  holder  and 
taxpayer  will  find  the  conclusions  which  will  prove  of  most  interest 
to  him  in  Chapters  I,  II,  and  XIV,  Summaries  of  III,  XIII,  XVI, 
and  XVII  to  XXIV1  relating  to  the  construction  of  pavements  and 
the  causes  of  their  deterioration.  The  relative  merits  of  various 
asphalts  for  paving  purposes  are  given  in  a  compact  form  at  the 
end  of  Chapter  XIV.  The  importance  of  the  action  of  water  on 
asphalt  in  Chapter  XXIII  2  The  resume  at  the  end  of  each  Chapter 
will  generally  furnish  the  reader  at  a  glance  with  an  opportunity 
of  determining  whether  the  details  in  that  Chapter  appeal  to  his 
interest  and  intelligence. 

THE  AUTHOR. 

NEW  YORK,  February  18,  1905. 

1  Second  Edition,  Chapter  XXV.      2  Second  Edition,  Chapte'  XXIV. 

iii 


248445 


PREFACE  TO   SECOND  EDITION. 


THE  very  flattering  reception  given  to  the  first  edition  of 
this  work,  resulting  in  an  exceedingly  large  sale  within  the  last 
three  years,  has  pointed  to  the  very  general  interest  in  the 
subject  treated  of,  by  the  persons  for  whom  the  book  was 
especially  intended.  In  consequence  of  the  very  considerable 
developments  in  the  industry,  it  has  seemed  desirable,  after  the 
exhaustion  of  the  second  impression  of  the  first  edition,  to  revise 
the  manuscript  completely,  and  to  bring  it  up  to  date.  This  has 
been  done  with  the  results  given  in  the  accompanying  pages. 

The  writer  is  indebted  to  Mr.  C.  N.  Forrest  for  a  revision  of  the 
matter  regarding  the  methods  of  analysis  which  are  described, 
and  for  many  other  suggestions. 

v 


TABLE   OF  CONTENTS. 


INTRODUCTION 1 

PART  I. 
THE  FOUNDATION  AND  INTERMEDIATE  COURSE. 

CHAPTER 

I.  THE  FOUNDATION  OR  BASE 3 

II.  THE  INTERMEDIATE  COURSE  .  - 19 

PART   II. 

THE  MATERIALS  CONSTITUTING  THE  ASPHALT  SURFACE 

MIXTURE. 

III.  THE  MINERAL  AGGREGATE 29 

IV.  FILLER,  OR  DUST 87 

V.  THE  NATURE  OF  THE  HYDROCARBONS  WHICH  CONSTITUTE  THE 

NATIVE  BITUMENS 97 

VI.  CHARACTERIZATION     AND     CLASSIFICATION     OF     THE     NATIVE 

BITUMENS 110 

PART   III. 
NATIVE  BITUMENS  IN  USE  IN  THE  PAVING  INDUSTRY. 

VII.  DIFFERENTIATION     AND    CHARACTERIZATION    OF    THE     NATIVE 

BITUMENS 115 

VIII.  PETROLEUMS 127 

IX.  THE  SOLID  BITUMENS 147 

vii 


Viii  TABLE  OF  CONTENTS. 

CHAPTER  PAGB 

X.  INDIVIDUAL  ASPHALTS • 156 

XI.  SOLID  NATIVE  BITUMENS  WHICH  ARE  NOT  ASPHALT 208 

XII.  ASPHALTIC  SANDS  AND  LIMESTONES 221 

XIII.  RESIDUAL  PITCHES,  OR  SOLID  BITUMENS  DERIVED  FROM  AS- 

PHALTIC AND  OTHER  PETROLEUMS 256 

XIV.  COMPARISON  OF  VARIOUS  NATIVE  ASPHALTS  AND  THEIR  RELA- 

TIVE MERITS  FOR  PAVING  PURPOSES 278 


PART   IV. 
TECHNOLOGY  OF  THE  PAVING  INDUSTRY. 

XV.  REFINING  OF  SOLID  BITUMENS 291 

XVI.  SURFACE  MIXTURES 313 

XVII.  ASPHALTIC  OR  BITUMINOUS  CONCRETE 375 

XVIII.  ASPHALT  BLOCKS 389 

XIX.  THE  PROCESS  OF  COMBINING  THE  CONSTITUENTS  INTO  A  SUR- 
FACE MIXTURE 395 

PART  V. 

HANDLING  OF  BINDER  AND  SURFACE  MIXTURE  ON  THE 

STREET. 

XX.  THE  STREET 412 

PART  VI. 
THE  PHYSICAL  PROPERTIES  OF  ASPHALT  SURFACES. 

XXI.  RADIATION,  EXPANSION,  CONTRACTION,  AND  RESISTANCE  TO 

IMPACT 425 

PART    VII. 

SPECIFICATIONS  FOR  AND  MERITS  OF  ASPHALT  PAVEMENT. 

XXII.  SPECIFICATIONS 435 

XXIII.  THE  MERITS  OF  THE  MODERN  SHEET-ASPHALT  PAVEMENT  ...  455 

XXIV.  ACTION  OF  WATER  ON  ASPHALT  PAVEMENTS 460 


TABLE  OF  CONTENTS. 


PART   VIII. 

CAUSES  OF  THE  DEFECTS  IN  AND  THE  DETERIORATION  OF 
ASPHALT  SURFACES. 

CHAPTER  PAGE 

XXV.  DEFECTS  IN  AND  DETERIORATION  OF  ASPHALT  PAVEMENTS  . .  471 
XXVI.  MAINTENANCE  OF  ASPHALT  PAVEMENTS 504 


PART   IX. 
CONTROL  OF  WORK. 

XXVII.  INSTRUCTIONS  FOR  COLLECTING  AND  FORWARDING  TO  THE 
LABORATORY  SAMPLES  OF  MATERIALS  IN  USE  IN  CON- 
STRUCTING ASPHALT  PAVEMENTS 509 

XXVIII.  METHODS  EXPLOYED  IN  THE  ASPHALT-PAVING  INDUSTRY  FOR 
THE   CHEMICAL   AND    PHYSICAL   EXAMINATION    OF   THE 

MATERIALS  OP  CONSTRUCTION 519 

XXIX.  SOLVENTS 589 

XXX.  EQUIPMENT  OF  A  LABORATORY  FOR  CONTROL  OF  ASPHALT 

WORK 595 

APPKNDIX.  599 


THE  MODERN  ASPHALT  PAVEMENT. 


INTBODUCTION. 

THE  object  of  this  work  is  to  demonstrate  the  nature  of  asphalt 
pavements  and  the  causes  of  defects  in  them,  to  bring  about  im- 
provement in  the  methods  of  their  construction,  and  to  show  how 
this  can  be  done. 

During  an  extended  experience  in  the  asphalt  paving  industry, 
which  has  included  the  inspection  of  the  construction  of  asphalt 
pavements  on  behalf  of  a  large  city  and  the  technical  supervision 
of  the  work  of  several  prominent  companies  which  contract  to 
lay  them,  it  has  been  forced  upon  the  attention  of  the  writer  that 
engineers,  and  others  who  are  interested  in  obtaining  the  best 
results,  have  not  been  made  sufficiently  acquainted  with  the 
technology  of  the  industry  and  with  the  importance  of  some  of 
the  engineering  details  involved  to  enable  them  to  differentiate, 
at  the  time  that  the  pavement  is  being  laid,  or  even  on  its  com- 
pletion, between  good,  bad,  or  medium  work.  Cities  have,  con- 
sequently, been  obliged  to  rely  on  the  statements  and  good  faith 
of  contractors,  with  the  result  that  many  asphalt  pavements  have 
eventually  proved  unsatisfactory,  although  when  completed  they 
were,  to  all  outward  appearance,  of  good  quality — a  condition  which 
might  have  been  readily  avoided  either  by  an  intelligent  super- 
vision of  the  materials  in  use  and  the  manner  of  handling  them, 
or  by  a  change  in  the  form  of  construction. 

It  is  proposed,  therefore,  to  describe  in  the  following  pages 
the  forms  of  construction  which  have  been  shown  by  experience 


2  THE  MODERN  ASPHALT  PAVEMENT. 

to  be  the  most  satisfactory,  the  character  of  the  materials  enter- 
ing into  the  composition  of  asphalt  pavements,  the  most  refined 
methods  used  in  the  industry  at  the  present  day  and  the  reasons 
which  have  led  to  their  adoption,  in  order  that  engineers  and 
others  who  are  responsible  for  the  supervision  and  character  of 
such  work  may  be  able  to  distinguish  between  that  of  good  and 
that  of  inferior  quality.  To  this  will  be  added  specifications  for 
asphalt  pavements  to  meet  various  environments  and  use,  and 
something  as  to  their  maintenance  and  the  causes  of  their  deterio- 
ration. 

The  conclusions  which  are  advanced  are  the  results  of  twenty 
years'  experience  in  the  industry  by  the  writer  with  pavements  in 
over  one  hundred  cities  in  the  United  States  and  in  several  in 
England,  Scotland,  and  France,  involving  the  construction  of 
between  twenty  and  thirty  million  yards  of  surface. 


PART  I. 

THE  FOUNDATION  AND  INTERMEDIATE  COURSE. 


CHAPTER  I. 
THE  FOUNDATION  OR  BASE. 

THE  modern  asphalt  pavement  in  its  perfected  state  is  the 
evolution  of  thirty  years  of  experiment  and  experience.  It  seems 
unnecessary  here  to  give  a  history  of  the  origin  of  this  form  of 
pavement  on  the  Continent  of  Europe,  or  of  the  earliest  experi- 
ments in  the  United  States  by  De  Smedt  with  artificial  mixtures 
of  sand  and  asphalt,  as  this  information  is  readily  available  in  numer- 
ous publications.  It  is  sufficient  to  take  the  subject  up  at  as  late 
a  date  as  1894,  when  the  first  successful  effort  was  made  to  place 
the  industry  on  a  rational  basis  as  distinguished  from  the  rule-of- 
thumb  methods  previously  in  vogue,  and  to  follow  it  down  to  the 
most  recent  practice. 

An  asphalt  pavement  consists  essentially  of  a  foundation  or 
support  for  the  surface  which  is  to  carry  the  traffic,  itself  supported 
by  the  soil,  and  a  surface  consisting  of  a  mineral  aggregate  cement- 
ed together  with  asphalt  to  protect  the  base  from  wear  and  disinte- 
gration, between  ;svhich  is  commonly  interposed  either  a  course  of 
broken  .stone  coated  with  bitumen,  known  as  binder,  or  some  sub- 
stitute for  it,  such  as  a  cushion  or  separate  course  of  the  surface 
material,  or  a  paint  coat  of  bitumen  dissolved  in  naphtha.  These 
three  elements  of  the  pavement  will  be  considered  in  turn. 

3 


4  THE  MODERN  ASPHALT  PAVEMENT. 

The  Subsoil  Base. — As  the  foundation  of  a  pavement,  of  any 
kind,  is  placed  upon  the  soil  and  supported  by  the  latter,  it  is  a 
matter  of  vital  importance  that  this  latter  support  should  be 
adequate,  and  it  will  only  prove  adequate  if  the  subsoil  is  not 
subject  to  displacement  from  settlement  or  frost  and  is  thoroughly 
drained. 

With  sandy  soils  which  are  well  compacted  and  which,  from 
their  nature,  are  well  drained  and  dry  there  is  no  difficulty  in  the 
preparation  of  a  satisfactory  subgrade.  Trenches  in  such  soils,  if 
they  occur,  can  be  solidly  refilled  with  the  aid  of  water.  If  the 
subgrade  is  a  true  sand,  as  in  the  neighborhood  of  seabeaches,  it 
may  be  necessary,  in  order  to  compact  the  surface,  to  spread  a 
course  of  gravel  between  the  sand  and  the  base  in  order  to  be  able 
to  roll  it  properly. 

With  clay  or  heavy  soils  it  is  much  more  difficult  to  prepare 
a  satisfactory  subgrade,  especially  if  this  is  likely  to  be  subjected 
to  the  action  of  frost  and  if  the  original  soil  has  been  much  dis- 
turbed by  trenches,  or  if  fills  occur.  If  the  subgrade  consists 
of  the  original  soil  in  situ,  the  only  consideration  necessary  is  its 
proper  drainage,  unless  there  are  soft  spots  due  to  local  causes, 
in  which  case  they  must  be  excavated  and  removed,  with  the  sub- 
stitution of  firm  for  the  softer  material.  The  satisfactory  back 
filling  of  trenches  in  a  heavy  soil  is  a  difficult  matter.  The  use 
of  water  is  a  disadvantage  in  such  work.  Heavy  soils  absorb 
and  hold  it  tenaciously  and  thus  prevent  thorough  compaction, 
final  settlement  only  taking  place  after  the  completion  of  the 
pavement.  Trenches  in  such  a  soil  should  be  carefully  and  slowly 
tamped  in  thin  layers. 

The  proper  drainage  of  heavy  clay  soils  is  an  essential  feature 
in  the  construction  of  a  satisfactory  pavement,  especially  where 
these  soils  are  apt  to  be  thrown  or  cracked  by  frost  in  very  cold 
climates,  a  condition  which  may  be  illustrated  by  that  occurring 
in  Manitoba,  where  cracks  frequently  open  in  the  ground  in 
winter,  from  four  to  six  inches  wide,  and  which  would  cause  cor- 
responding cracks  in  the  asphalt  surface  were  not  some  provision 
made  against  it.  For  this  purpose  a  form  of  construction  has 
been  evolved  which  has  proved  quite  successful  by  providing  sat- 
isfactory drainage  and  not  laying  the  hydraulic  concrete  foundation 


THE  FOUNDATION.  5 

in  direct  contact  with  the  subsoil.  Upon  the  subsoil  clean  sand 
and  gravel  are  spread  and  rolled  to  a  depth  of  three  inches, 
and  upon  this  the  hydraulic  concrete  foundation  is  laid.  At  the 
same  time,  at  intervals  of  twenty-five  feet,  trenches  are  cut 
in  the  subsoil  to  a  depth  of  six  inches,  and  filled  with  coarse 
broken  stone;  these  cross-drains  being  connected  with  similar 
trenches,  containing  coarse  broken  stone,  under  the  curb,  which 
are  graded  to  catch-basins  for  the  removal  of  water.  In  such  a 
climate  tile  drains  cannot  be  used  successfully,  the  author  is 
informed  by  the  City  Engineer  of  Winnipeg,  because  the  ground 
is  generally  frozen  when  the  surface-water  first  begins  to  drain 
away  and  this  water  filling  the  tile  often  freezes  and  bursts  it. 
The  provisions  in  use  in  Winnipeg  seem  to  be  an  ideal  way  of 
treating  heavy  soils  in  cold  climates  and,  although  absolutely 
necessary  in  such  a  location,  are  extremely  desirable  where  any 
soil  of  such  a  description  is  found.  Further  details  in  regard 
to  this  method  will  appear  in  the  chapter  on  "Specifications."  l 

When  a  street  is  terraced  and  the  roadway  is  lower  than  the 
adjacent  property  the  greatest  precaution  should  be  taken  to 
prevent  the  seepage  from  higher  levels  from  working  down  between 
the  soil  and  the  foundation,  or  between  the  foundation  and  surface. 
For  this  purpose  drainage  6hould  be  provided  below  or  along  the 
curb,  and  at  times  ia  the  subsoil  itself. 

The  most  serious  subgrade  to  encounter  as  a  support  for  a 
foundation  is  marshy  or  swampy  land,  fills  made  on  the  latter  for 
the  purpose  of  raising  the  grade,  or  even  fills  on  ordinary  soils  where 
sufficient  time  has  not  elapsed  to  bring  about  final  settlement  and 
ultimate  compaction.  Where  such  conditions  are  unavoidable 
good  practice  calls  for  the  use  of  a  sufficiently  strong  hydraulic 
concrete  foundation  to  bridge  over  irregular  settlement  and  to 
distribute  the  load  over  weak  points. 

The  cause  of  much  of  the  deterioration  in  asphalt  surfaces 
and  in  otner  pavements  is  due  to  a  neglect  of  such  precautions 
in  regulating  the  subgrade  or  in  providing  a  foundation  of  a 
character  to  bridge  over  defects  in  the  latter. 

1  Page  435. 


6  THE  MODERN  ASPHALT   PAVEMENT. 

It  seems  hardly  necessary  to  state  that  any  subsoil  should  be 
thoroughly  compacted  by  a  heavy  roller  of  broad  tread,  and  that 
any  weak  portions  revealed  by  the  use  of  such  roller  should  be 
removed  by  treatment  in  an  appropriate  way. 

The  Foundation. — Foundations  of  most  varied  character  have 
been  used  in  the  construction  of  pavements,  including  broken  stone 
with  or  without  a  coating  of  more  or  less  bitumen  or  coal-tar,  mac- 
adam, old  cobblestone  pavement,  an  old  surface  of  granite  blocks 
or  blocks  turned  and  reset,  old  brick  or  asphalt-block  surfaces,  and 
hydraulic  concretes  of  natural  or  Portland  cement  of  varying  thick- 
ness. Each  of  these  forms  has  been  more  or  less  successful  under 
different  conditions,  consideration  being  given  to  economy,  to 
local  environment,  and  to  the  traffic  to  be  carried. 

Bituminous  Foundation. — The  so-called  bituminous  founda- 
tion possesses  no  advantage  save,  in  some  cases,  that  of  economy. 
It  has  been  almost  entirely  abandoned  as  a  support  for  asphalt 
surfaces.  It  is  a  relic  of  the  days  when  hydraulic  cement  was  a 
much  more  expensive  article  than  at  the  present  time.  As 
generally  constructed  it  consists  of  six  or  more  inches  of  broken 
stone  passing  a  two  or  two  and  one-half-inch  ring  and  not 
containing  any  particles  passing  a  one  or  one  and  one-half-inch 
ring.  Stone  of  such  uniform  size  contains  a  large  volume  of 
voids,  forty  per  cent  or  over,  and  does  not  compact  well.  Were 
it  the  run  of  the  crusher,  the  foundation  would  be  far  more  satis- 
factory. Under  the  roller  much  of  the  stone  is  often  lost  in  the 
subsoil  before  the  required  thickness  is  attained.  The  coating  of 
bitumen  applied  to  the  surface  of  the  foundation  is  of  little  or  no 
advantage.  Enough  cannot  be  used  to  fill  the  voids,  as  if  this  is 
done  the  excess  will  be  drawn  up  into  the  surface  by  a  hot  sun 
and  destroy  or  soften  the  latter  while  the  cost  would  also  be 
prohibitive. 

Additional  disadvantages  of  such  a  foundation  are  that  it  pos- 
sesses no  rigidity  or  stability  and  consequently  responds  at  once  to 
any  settlement  or  weakness  of  the  subsoil;  that  it  is  porous  and 
allows  the  free  movement  of  water  and  gas,  and  that  the  binder  and 
surface  cannot  be  readily  removed  from  it  for  renewal  without 
its  destruction. 


THE  FOUNDATION.  7 

Excellent  asphalt  pavements  have  been  constructed  with  a 
bituminous  foundation  where  the  subsoil  was  firm  and  resistant 
and  the  travel  light,  as  is  the  case  in  many  residence  streets,  but 
surfaces  equally  good  have  been  laid  with  broken  stone  alone. 
The  cost  of  renewal  of  the  surface  of  such  pavements  is,  however, 
high,  as  has  already  been  shown. 

Macadam  Foundation. — Old  macadam  has  been  used  success- 
fully in  several  instances  as  a  foundation  for  asphalt  pavement.  It 
possesses  many  advantages  over  broken-stone.  In  macadam  the 
voids  in  the  stone  are  well  filled  with  finer  particles  and  it  has 
received  its  ultimate  compression  under  travel.  It  has  not  a 
coating  of  bitumen,  so  that  the  binder  and  surface  coats  are  readily 
removed  for  renewal.  It  possesses  the  defect  that  the  grade  of 
the  macadam  can  be  altered  but  slightly  without  serious  disturb- 
ance of  its  bond,  and  in  replacing  the  pavement  over  trenches  the 
stone  becomes  far  less  of  a  support  than  the  original  macadam. 
It,  of  course,  presents  the  merit  of  economy.  An  excellent  example 
of  an  asphalt  pavement  with  a  foundation  of  this  class  is  to  be  seen 
on  Broadway,  above  Fifty-ninth  Street,  in  New  York  City,  and  on 
Michigan  Avenue,  to  the  south  of  Congress  Street,  in  Chicago, 
111.  The  former  street  has  been  trenched  to  a  large  extent,  and 
repairs  have  resulted  very  satisfactorily.  The  latter  has  a  few 
cracks  owing  to  the  action  of  frost. 

Other  Old  Pavement  as  Foundation. — Old  cobblestone  and 
asphalt-block  pavements  form  an  excellent  foundation  for  asphalt 
pavements  if  the  height  of  curb  shown  is  sufficient  and  the  amount 
of  traffic  permits.  They  should  not  be  used  if  resetting  is  necessary 
except  on  very  favorable  soil  and  with  the  expectation  of  very 
moderate  use. 

Old  granite-block  pavements  have  been  very  extensively  used 
for  supporting  asphalt  surfaces,  especially  in  New  York  City, 
and  their  value  for  this  purpose  and  the  defects  which  result  there- 
from are  well  illustrated  there.  Granite  blocks  laid  in  sand  on 
the  soil  have  been  found  very  satisfactory  on  cross-town  residence 
streets,  but  have  been  most  unsatisfactory  on  streets  like  First 
Avenue,  where  the  subsoil  is  soft,  fills  are  frequent,  and  partly  on 
land  below  high-water  mark,  in  bringing  the  street  originally  to 


S  THE  MODERN  ASPHALT  PAVEMENT. 

grade.  These  blocks  could  be  seen  to  move  under  the  steam-roller 
when  the  binder  course  was  laid,  and  the  asphalt  surface  is,  in  con- 
sequence, in  constant  need  of  repairs.  The  only  foundation  which 
would  prove  satisfactory  under  these  conditions  would  be,  con- 
sidering the  heavy  travel  on  the  street,  the  best  form  of  Portland- 
cement  concrete  to  a  depth  of  at  least  eight  inches. 

Granite  blocks  on  concrete  make  an  excellent  foundation  for 
an  asphalt  surface,  if  not  reset,  but  where  the  grade  necessitates 
taking  them  up  and  replacing  them  on  their  broad  sides  the  result 
is  not  satisfactory  except  on  residence  streets.  When  relaid  they 
are  not  rigid,  but  have  a  tendency  to  rock  under  heavy  travel. 
Such  a  foundation  supports  the  asphalt  surface  on  Broadway  and 
several  avenues  in  New  York  City,  and  has  not  been  entirely 
successful.  The  turned  blocks  were  opened  to  travel  for  some  time 
to  bed  them  thoroughly,  and  any  loose  ones  reset.  The  binder 
and  surface  were  then  laid  directly  on  the  blocks.  The  vibration 
on,  these  blocks,  especially  along  the  rail,  is  nevertheless  large. 
A  better  form  of  construction  would  be  to  grout  the  blocks,  after 
turning,  with  Portland  cement,  and  keep  traffic  off  of  them  until 
the  grout  is  set.  The  lesson  is  that  turned  granite  blocks  should 
not  be  used  as  a  foundation  for  asphalt  pavements  on  streets  of 
heavy  travel,  even  when  supported  by  Portland-cement  concrete, 
and  much  less  so  on  soil  alone,  as  has  recently  been  done  on 
Fourth  Avenue  in  New  York  City. 

Construction  of  this  description  inevitably  results  in  deteriora- 
tion of  the  best  asphalt  surfaces,  with  the  results  that  the  defects 
are  attributed  to  the  asphalt  and  not  to  the  foundation  where  they 
really  originate.  As  a  matter  of  fact  no  foundation  is  suitable  for 
a  street  of  heavy  travel  except  one  of  Portland-cement  concrete 
of  sufficient  depth  and  strength  to  carry  the  load  imposed  upon  the 
surface  with  perfect  rigidity,  and  it  is  equally  true,  as  determined 
by  years  of  careful  observation,  that  ninety  per  cent  of  the  defects 
in  asphalt  pavements  in  such  cities  as  New  York,  where  the  sur- 
face mixture  is  of  standard  quality,  are  due  to  the  insufficiency 
of  the  foundation. 

Old  brick  pavements  have  served  as  a  support  for  asphalt  sur- 
faces with  entire  satisfaction.  They  have  received  the  full  traffic 
of  the  street  to  be  resurfaced  and  are  therefore  well  compacted. 


THE  FOUNDATION.  9 

Such  pavements,  as  their  surfaces  become  too  uneven  for  use,  will, 
in  the  future,  be  largely  renewed  in  this  way. 

Hydraulic-Concrete  Foundation. — Hydraulic  concrete,  if  prop- 
erly proportioned,  made  with  good  cement  and  a  well-graded 
aggregate,  well  mixed  and  put  in  place  satisfactorily  and  in  good 
weather,  is  the  ideal  foundation.  Unfortunately  these  conditions 
are  not  always  met.  To  discuss  the  possible  variations  and  de- 
ficiencies in  detail  would  be  to  write  an  elaborate  treatise  on  the 
subject  of  concrete.  It  will  suffice,  however,  to  point  out  the  chief 
merits  and  defects  which  appear  most  strongly  in  its  use  as  a 
foundation  for  pavements. 

The  proportions  of  the  different  constituents,  from  which  the 
contractor  cannot  depart,  are  sometimes  injudiciously  prescribed, 
and  usually  from  motives  of  economy.  In  an  eastern  city  a 
concrete  foundation  is  specified  which  is  to  consist  of  one  (1)  part 
of  Portland  cement,  four  (4)  parts  of  sand,  frwe  (5)  p.arts  of  gravel, 
and  five  (5)  parts  of  stone.  While  such  a  foundation  may  have 
sufficient  strength  to  support  a  pavement  carrying  moderate  travel, 
it  is  nevertheless  porous  and  permits  of  the  free  movement  of  water 
and  gas  from  below,  both  of  which  act  on  asphalt  under  such 
circumstances.  The  most  favorable  proportions  which  the  writer 
has  observed  for  a  concrete  for  heavily  travelled  streets  are  those 
which  were  prescribed  for  Fifth  Avenue,  in  New  York  City,  in  1896. 
These  were:  one  (1)  part  of  Portland  cement,  three  (3)  parts  of 
sand,  two  (2)  or  three  (3)  parts  of  gravel,  and  four  (4)  or  five  (5) 
parts  of  broken  stone.  If  the  stone  were  large  the  larger  amount 
of  gravel  was  used  and  the  reverse.  The  gravel  in  the  preceding 
concrete  is  of  the  greatest  aid  in  filling  the  voids  in  the  stone  and 
in  facilitating  the  compaction  of  the  concrete  when  rammed.  Stone 
with  sand  alone  is  very  apt  to  bind,  bridge,  and  resist  compaction, 
while  the  voids  are  so  large  as  to  leave  at  times  a  portion  of  them 
unfilled  with  mortar. 

The  foundation  thus  constructed  on  Fifth  Avenue  has  a  depth 
of  at  least  seven  inches  and  is  absolutely  rigid.  The  asphalt  sur- 
face placed  on  this  is  subject  to  no  vibration  and  has  shown  no 
deterioration  due  to  this  cause  in  twelve  years,  while  the  same 
surface  mixture  supported  only  by  the  granite  blocks  on  a  soft 
soil  in  First  Avenue  was  in  far  from  good  condition  in  a  vear. 


10  THE   MODERN  ASPHALT  PAVEMENT. 

This  contrast  between  the  two  avenues  with  their  different  founda- 
tions is,  therefore,  most  instructive  and  points  to  the  fact  that  the 
primary  consideration  in  an  asphalt  pavement  is  the  foundation 
which  supports  it.  Without  a  rigid  one  the  best  of  materials  and 
workmanship  in  the  remainder  of  the  pavement  will  go  for  naught. 

Ordinary  practice  as  regards  the  aggregate  in  a  hydraulic 
concrete  provides  for  broken  stone  all  of  which  "will  pass  in  any 
direction  through  a  revolving  circular  screen  having  holes  two  and 
one-half  (2^)  inches  in  diameter  and  be  retained  by  a  screen  hav- 
ing holes  one  (1)  inch  in  diameter."  1  This  may  be  good  prac- 
tice, but  is  certainly  not  the  best. 

The  grading  of  the  broken  stone  is  an  important  consideration 
in  adjusting  the  relations  of  the  constituents  in  a  well-proportioned 
concrete  not  only  in  a  foundation  for  asphalt  pavements,  but  in  its  use 
far  every  purpose.  Fortunately  this  is.  rapidly  becoming  recognized. 
As  has  already  been  mentioned,  the  voids  in  broken  stone  passing 
a  two-inch  ring  and  not  passing  an  inch  and  one-half  or  a 
one-inch  ring  are  very  large  in  volume,  and  it  has  been,  and 
generally  is,  the  practice  to  attempt  to  fill  them  with  a  mortar  of 
one  part  of  cement  and  three  parts  of  sand,  in  the  case  of 
Portland,  or  two  in  the  case  of  natural  cement.  This  is  not 
economical  in  more  ways  than  one.  It  is  much  better  to  reduce 
the  voids  by  using  the  broken  stone  as  it  comes  from  the  crusher 
in  well-assorted  sizes  and  with  smaller  voids,  the  screenings  passing 
a  quarter-  or  three-eighth-inch  screen  only  being  removed,  on 
account  of  its  tendency  to  segregate  and  because  it  should  actually 
be  considered  as  sand,  as  will  appear  later,  or  to  add  gravel  where 
it  is  available  or  where  economy  demands  the  separation  of  the 
inch  stone  for  use  in  binder.  The  mortar  then  goes  much  farther, 
is  not  in  such  large  masses,  and  the  concrete  is  rammed  and  com- 
pacts with  much  greater  ease.  Under  such  circumstances,  while 
the  proportion  of  cement  and  sand  should  not  be  extended  beyond 
one  of  the  former  to  three  of  the  latter,  corresponding  to  the 
relation  of  the  volume  of  the  cement  to  the  voids  in  the  average 
concrete  sand,  the  proportion  of  stone  to  the  mortar  may  be  largely 

1  Manhattan  (New  York)  Specifications,  1901,  paragraph  12. 


THE  FOUNDATION.  11 

extended  beyond  that  which  may  be  safely  allowed  for  stone  of 
uniform  size  and  large  voids. 

Where  good  gravel  is  available,  containing  particles  of  suf- 
ficiently large  size,  a  concrete  made  with  this  material  without  the 
use  of  crushed  stone  may  be  as  equally  satisfactory  or  even  preferable 
to  one  constructed  with  stone  alone  or  with  a  mixture  of  stone  and 
gravel.  A  provision  for  such  concrete  is  now  contained  in  the  speci- 
fications of  some  of  our  cities. 

Where  gravel  occurs  mixed  with  the  requisite  proportion  of 
sand  such  a  natural  mineral  aggregate  can  be  employed  in  the 
manner  in  which  Thames  ballast  is  used  in  London,  England,  and 
with  the  most  satisfactory  results.  The  occurrence  of  such  deposits 
in  the  United  States  is  exceptional. 

Another  fortunate  thing  in  recent  practice  is  the  recognition 
of  the  facts  that  a  concrete  the  mortar  in  which  is  wet  enough  to 
almost  quake  under  the  tamper  gives  the  most  satisfactory  results, 
since  the  slight  early  loss  in  strength  due  to  the  water  excess  is 
more  than  made  up  by  the  improved  and  thorough  compaction 
attained.  Dry  concrete  is  no  longer  regarded  as  good  prac- 
tice. 

In  the  early  days  of  the  asphalt-paving  industry  hydraulic 
concrete  was  usually  mixed  by  hand  labor  on  boards.  To-day 
much  of  this  work  is  very  satisfactorily  and  much  more  cheaply 
done  with  the  use  of  mixers  driven  by  power.  Of  these  there  are 
a  number  of  successful  types  now  on  the  market,  and,  from  the 
author's  observation,  they  are  strongly  to  be  recommended  where 
the  extent  of  the  work  will  justify  their  being  employed. 

Concrete  Sand. — It  is  usually  specified  that  sand  in  use  in 
concrete  shall  be  clean,  coarse,  sharp,  and  free  from  loam  and  dirt. 
The  degree  of  coarseness  is  generally  somewhat  indefinitely  expressed. 
Concrete  sand  as  a  rule  contains  but  a  small  percentage  of  grains 
finer  than  will  pass  a  fifty-mesh  sieve.  It  may,  however,  con- 
tain to  advantage  a  considerable  portion  of  fine  gravel.  In  this 
connection  it  may  be  remarked,  however,  that  the  permeability 
of  a  concrete  is  greater  the  coarser  the  sand,  and  that  the  presence 
of  some  fine  grains  is  not  undesirable.  A  small  amount  of  loam 
or  clay  in  sand  is  not  injurious  if  it  is  not  present  in  a  lumpy  con- 


12  THE  MODERN   ASPHALT  PAVEMENT. 

dition.  Many  pit  sands  which  have  been  rejected  on  account  of 
the  presence  of  loam  make  excellent  concrete. 

Crusher  Screenings.— Sand  has  been  defined  as  the  detritus 
of  rock,  smaller  than  gravel  and  larger  than  silt.  Under  such  a 
definition  the  screenings  from  the  crushing  of  rock  for  the  pro- 
duction of  broken  stone  is  sand  and  may  be  used  as  such  in  concrete. 
Its  use  for  such  purposes  has  attracted  very  considerable  attention 
recently,  and  the  results  obtained  with  it  have  been  most  successful. 
The  strength  of  the  concrete  in  which  sand  is  replaced  by  screenings 
is  always  equal  to  and  in  many  cases  in  excess  of  that  made  with 
natural  sand.  It  has  been  used,  and  pronounced  a  desirable 
material,  in  the  concrete  of  the  Buffalo  breakwater,1  in  the  Man- 
chester and  Liverpool  (England)  water-works,2  in  the  Jerome 
Park  Reservoir  in  New  York  City,  in  masonry  construction  on  the 
C.  M.  &  St.  P.  R.  R.,  and  in  the  concrete  on  the  Water-power 
Sections  Nos.  1,  2,  and  3  of  the  Chicago  Drainage  Canal.  It  has 
been  tested  by  many  engineers  in  the  laboratory  and  found  to 
produce  concrete  exceeding  or  equalling  in  strength  that  made  with 
sand.  An  excellent  resume  of  the  availability  of  this  material 
will  be  found  in  "The  Cement  Age,"  Vol.  l,.No.  3,  page  5,  August 
1904,  and  in  a  publication  of  the  Producers'  Supply  Company, 
entitled  "Crushed  Stone  and  its  Uses/'  pages  100,  103,  and  107, 
Chicago,  1904. 

It  has  been  successfully  used  in  the  concrete  foundation  for  asphalt 
pavements  in  several  cities,  and  its  use  for  this  and  other  purposes 
is  rapidly  increasing.  The  author  made  the  following  statement 
in  connection  with  the  use  of  crusher  screenings  as  a  witness  before 
the  Aqueduct  Commissioners  of  the  City  of  New  York  when  this 
was  objected  to  by  the  Merchants'  Association  of  the  city: 

"The  advantages  are  that  the  particles  in  the  crusher  screen- 
ings are  better  graded  in  size,  and  in  consequence  those  screenings 
have  a  smaller  volume  of  voids  or  unfilled  cavities  in  them.  As 
a  result  a  definite  volume  of  Portland  cement  will  go  farther 
towards  filling  those  voids  than  with  sand,  where  the  particles 

1  Eng.  News,  Sept.  11,  1902. 

2  Hill,  Institution  of  Civil  Engineers,  London,  1896;  Deacon,  ibid. 


THE   FOUNDATION.  13 

are  more  uniform  in  size  and  the  volume  of  the  voids  large.  .    .    . " 
There  can  be  no  question  that  crusher  screenings  are  preferable 
to  many  natural  sands  when  the  rock  in  which  they  originate  is 
of  desirable  quality. 

Character  of  the  Hydraulic  Cement  in  Use. — The  character  of 
the  hydraulic  cement  in  use  in  concrete  foundations  is  as  important 
as  any  constituent  of  the  pavement.  If  it  is  defective  in  any  way, 
the  result  will  be  shown  in  the  surface.  In  one  case  one  of  the 
most  prominent  surfaces  in  the  country  became  cracked  across 
the  street  at  wide  intervals  two  years  after  it  was  laid,  and  in  three 
years  the  surface  was  noticeably  raised  at  these  points.  On  open- 
ing the  pavement  the  cracks  in  the  surface  were  found  to  be  due 
to  cracks  in  the  concrete  formed  during  the  first  two  years,  and 
the  elevation  of  the  surface,  which  occurred  later,  to  the  subse- 
quent expansion  of  the  cement,  which  in  this  way  pushed  one 
portion  of  the  foundation  upward  and  over  the  other,  although  the 
cement  was  a  Portland  and  one  which  responded  satisfactorily  to 
all  short-time  tests  for  constancy  of  volume.  A  similar  exper- 
ience was  met  with  for  several  years  with  the  natural  cements  of 
western  New  York,  and  it  was  generally  necessary,  where  one 
brand  was  used,  to  remove  the  surface  and  cut  out  the  expanded 
portion  after  a  few  years  in  order  to  bring  the  surface  of  the 
pavement  to  grade. 

In  the  middle  West  serious  troubles  due  to  the  character  of 
the  natural  cement  in  use  were  often  met  with  befoie  Portland 
cement  became  available.  The  natural  cements  of  that  part  of  the 
country  are  not  always  reliable  or  uniform  and  are  especially  un- 
suited  for  use  in  cold  weather,  as  they  fail  to  set  when  the  tem- 
perature approaches  freezing.  The  writer  has  frequently  seen 
hydraulic  foundations  which  have  acquired  no  bond,  either  from 
their  inferior  quality  alone  or  because  of  use  in  cold  weather.  Such 
a  foundation  is  open  and  porous  and  allows  water  to  reach  and 
disintegrate  the  asphalt  surface.  It  frequently  cracks  after  a  firm 
set  has  taken  place,  and  these  cracks  are  eventually  repeated  in  the 
asphalt  surface,  as  can  be  seen  in  the  accompanying  illustration, 
Fig.  1 .  The  evident  conclusion  is  that  the  use  of  natural  cement 
in  concrete  for  the  foundation  of  asphalt  pavements  should  be 


FIG.  1. 


14 


THE   FOUNDATION  15 

abandoned,  although  it  would  not  be  justifiable  to  suppose  that 
none  made  from  this  cement  or  even  the  majority  of  it  is  poor. 
That  under  the  first  asphalt  pavement  of  any  area,  on  Pennsyl- 
vania Avenue,  Washington,  D.  C.,  was  constructed  with  natural 
cement  from  the  Potomac  Valley,  and  during  thirty  years  gave 
entire  satisfaction.  Foundations  containing  the  Rosendale  cem- 
ents have  proved  equally  good,  but  all  the  natural  cements  of 
this  description  attain  their  strength  so  slowly  that  an  unfortu- 
nately long  period  must  elapse  before  they  will  safely  sustain  a  heavy 
roller  suitable  for  compressing  the  binder  and  surface,  and  in  this 
way  the  completion  of  the  pavement  is  delayed.  It  is  therefore 
much  better  to  avoid  using  natural  cements,  and  the  substitution 
of  Portland  cement  has  become  the  very  general  practice. 

All  hydraulic  cement  in  use  in  the  construction  of  asphalt 
pavements  should  be  tested  before  it  is  allowed  to  go  into  the 
work,  and  should  meet  the  requirements  which  the  local  engineer 
believes  to  be  reasonable.  The  Committee  on  Uniform  Tests  of 
Cement  of  the  American  Society  of  Civil  Engineers  has  recom- 
mended methods  which  should  bring  about  greater  uniformity 
in  testing  cements,  and  their  use  is  suggested.1 

A  similar  committee  of  the  American  Society  for  Testing  Mate- 
rials has  recommended  reasonable  specifications  for  cement  which 
can  be  adopted  if  they  meet  with  the  approval  of  the  engineer.2 

Lateral  Support. — Closely  related  in  importance  to  the  char- 
acter of  the  foundation  of  the  pavement  is  that  of  the  lateral  sup- 
port which  the  surface  receives. 

It  is  quite  as  well  proved  by  experience  that  more  defects 
in  asphalt  surfaces  are  due,  proportionally  to  the  area  involved, 
to  the  lack  of  this  than  to  weak  foundation  and,  often,  to  all  other 
causes. 

The  lateral  support  should  be  as  rigid  as 'in  the  case  of  the 
foundation,  and  unfortunately  it  is  not  always  so  about  manholes, 
water-  and  gas-boxes,  at  headers  where  the  surface  ends,  and  espe- 
cially against  rails.  Vibration  about  manholes,  boxes,  etc.,  can  be 

1  Proceedings  Am.  Soc.  C.  E.,  1903,  29,  No.  1. 

1  Report  of  Committee  C  on  Standard  Specifications  for  Cement.  Pre- 
sented at  Annual  Meeting,  1904,  June  17. 


16  THE  MODERN  ASPHALT  PAVEMENT. 

avoided  by  providing  heavy  castings  with  a  broad  base  and  set- 
ting them  upon  a  proper  foundation  in  Portland  cement  a  suffi- 
ciently long  period  before  laying  the  surface  to  prevent  them  from 
being  loosened  by  a  blow  from  the  roller.  Headers  should  be 
sufficiently  heavy  to  hold  the  surface  up  and  resist  the  impact 
of  traffic. 

The  construction  of  a  street  car-track  the  rails  and  sleepers 
of  which  shall  be  sufficiently  free  from  vibration  to  form  a  sup- 
port for  an  immediately  adjacent  asphalt  surface  is  a  most  diffi- 
cult matter  and  one  that  is  rarely  successfully  carried  out,  espe- 
cially when  trolley-cars  of  the  size  and  weight  of  those  in  use 
to-day  are  to 'be  considered. 

Experience  has  shown  that  construction  involving  the  use  of 
a  very  heavy  girder-rail  placed  upon  ties,  which,  together  with 
the  rail,  are  embedded  in  concrete  from  the  base  of  the  former 
to  the  height  of  the  adjoining  foundation  of  the  pavement,  is  the  best. 
Such  construction  will  be,  however,  of  little  value  if  traffic  is 
allowed  over  the  rail  before  the  concrete  has  had  time  to  set  thor- 
oughly. In  cases  where  the  soil  is  very  heavy  and  the  drainage 
is  bad  crushed  stone  used  as  ballast  may  often  prove  more  satis- 
factory than  hydraulic  concrete,  as  affording  better  drainage. 
Where  mud  forms,  owing  to  poor  drainage,  and  works  into  cracks 
between  the  asphalt  surface  and  the  concrete  the  result  is  very 
disastrous. 

Another  form  of  rail  construction  which  has  met  with  con- 
siderable approval  is  the  placing  of  the  rail  upon  a  hydraulic  con- 
crete beam  extending  its  entire  length.  It  is  possible  that  this 
may  be  desirable  where  carefully  carried  out,  but,  in  the  author's 
experience,  where  a  girder-rail  of  sufficiently  heavy  type  is  to  be 
used  no  advantage  is  derived  commensurate  with  the  expense,  and 
the  possibility  of  vibration  is  not  lessened. 

If  vibration  still  takes  place  in  a  rail,  even  with  the  best  form 
of  construction,  and  this  is  rarely  absent  with  heavy  trolley-cars, 
a  triple  row  of  the  best  paving-blocks,  or  bricks,  laid  with  broken 
joints  parallel  to  the  rail  should  be  placed  against  it,  bedded  in 
cement,  and  well  grouted,  depressing  the  base  sufficiently  for 
this  purpose.  Header  and  stretcher  construction  is  most  faulty. 
The  asphalt  toothing  is  then  a  point  of  weakness. 


THE  FOUNDATION.  17 

Vibration  of  the  rail  will  eventually  destroy  an  immediately 
adjoining  surface  not  only  by  breaking  the  bond  between  the 
particles  of  the  surface,  but  by  admitting  water  and  mud  after 
the  first  fracture  has  taken  place. 

All  the  defects  which  are  due  to  weakness  in  the  foundation  and  to 
the  lack  of  lateral  support  involve  not  only  an  expense  to  the 
contractor  during  the  guarantee  period  which  he  must  consider 
hi  his  bids  after  a  study  of  the  form  of  construction  specified  by 
the  city,  but  will  also  prove  an  additional  cost  to  the  city  when 
it  takes  over  the  maintenance  of  the  street.  Economy  in  the  cost 
of  the  pavement  in  this  direction  may  not  prove  true  economy 
in  the  end. 

While  it  is  not,  of  course,  necessary  that  a  needlessly  expen- 
sive foundation  should  be  provided  for  an  asphalt  pavement,  it  will 
eventually  prove  cheaper  if  a  good  margin  of  safety  in  this  direc- 
tion is  allowed.  An  asphalt  surface  is  no  stronger  than  its  weak- 
est part. 

SUMMARY. 

It  appears  that  better  concrete  can  be  made  of  graded 
broken  stone  than  of  stone  of  uniform  size,  that  the  addi- 
tion of  gravel  is  an  improvement,  that  a  concrete  consisting  of 
gravel  alone  as  a  substitute  for  broken  stone  will  often  prove  sat- 
isfactory, that  crusher  screenings  are  an  excellent  substitute  for 
natural  sand,  that  Portland  cement  is  infinitely  preferable  to 
natural  cement,  that  the  greatest  care  should  be  used  that  the 
pavement  should  have  a  proper  lateral  as  well  as  vertical  support, 
and  that  the  greatest  attention  should  be  paid  to  the  rigidity  of 
railroad-track  construction. 

It  seems,  therefore,  that  while  an  asphalt  pavement  of  the 
best  quality  can  be  constructed  only  when  all  its  elements — foun- 
dation, binder  or  its  substitute,  and  surface — are  of  the  highest  degree 
of  perfection,  refinement  in  the  character  of  the  binder  and  sur- 
face is  thrown  away  if  the  subsoil  is  not  satisfactorily  drained  and 
if  the  foundation  of  the  pavement  is  not  sufficiently  strong  to  carry 
the  traffic  to  which  the  surface  is  subjected  with  entire  rigidity 


18  THE  MODERN  ASPHALT  PAVEMENT. 

and  is  not  sufficiently  impervious  to  protect  the  surface  from  the 
action  of  water  and  illuminating-gas. 

In  addition  a  well-constructed  foundation  is  a  matter  of 
economy,  as  it  should  last  for  all  time  and  will  only  require 
resurfacing  at  intervals,  whereas  an  inferior  one  must  eventually 
be  renewed  by  one  properly  constructed. 


CHAPTER  II. 
THE  INTERMEDIATE  COURSE. 

IN  the  early  days  of  the  asphalt-paving  industry  a  thicker 
wearing  surface  was  hi  use  than  to-day.  That  of  1876  on  Pennsyl- 
vania Avenue  in  Washington,  D.  C.,  and  most  of  those  laid  in  the 
following  fifteen  years  were  two  and  one-half  niches  thick.  These 
surfaces  were  laid  in  two  courses,  and  are  thus  described  in  an 
old  specification  of  a  Washington  contractor  in  1878: x 

"The  asphalt  (surface  mixture),  having  been  prepared  in  the 
manner  thus  indicated,  is  laid  on  the  foundation  in  two  coats. 

"The  first  coat  of  one-half  inch  thickness,  called  protecting 
coat,  might  be  laid  richer  in  asphaltic  cement,  and  may  be  consoli- 
dated simply  by  rolling  with  iron  or  stone  rollers  weighing  about 
1000  pounds  or  half  a  ton. 

"On  this  first  asphalt  coat  is  then  carefully  spread  with  iron 
rakes  the  final  finishing  coat,"  etc.,  etc. 

It  is  evident  from  this  that  the  one-half-inch  coat  of  surface 
mixture  was  laid  for  no  other  purpose,  at  this  tune,  than  to  pro- 
tect the  rather  friable  hydraulic  concrete  of  natural  cement  from  being 
broken  up  by  hauling  the  final  surface  mixture  over  it.  It  will 
be  noted  that  it  is  suggested  to  lay  the  first  coat  of  material  richer 
in  asphalt  cement. 

In  1884  the  specifications  which  the  city  itself  adopted  were 
evidently  based  on  those  of  1878,  but  the  wording  was  somewhat 
changed,  "pavement  mixture"  replacing  "asphalt"  in  the  first 
paragraph  quoted,  and  " cushion  coat"  for  "protective  coat,"  with 
some  other  minor  alterations,  in  the  second,  the  thickness  of  the 

1  Rept.  of  Com.  D.  C.f  1878,  292. 

19 


20  THE  MODERN  ASPHALT  PAVEMENT. 

latter  remaining  one-half  inch  "after  being  consolidated  by  a 
roller,"  while  it  is  to  contain,  specifically,  "from  two  to  four  per 
cent  more  asphaltic  cement"  than  the  "surface  coat." 

In  the  interval  mentioned  the  term  "protective  coat"  which 
casts  some  reflection  on  the  character  of  the  foundation  has,  therefore, 
been  changed  to  "cushion  coat."  The  greater  richness  of  the  cush- 
ion has  been  retained. 

In  the  specifications  for  1886-87  no  mention  is  made  of  a  pro- 
tective or  cushion  coat.  It  is  provided  that  the  surface  mixture 
will  be  "carefully  spread,  in  such  a  manner  as  to  give  a  uniform 
and  regular  surface  and  to  such  depth  as,  after  having  received 
its  ultimate  compression  of  40  per  cent,  to  have  a  thickness  of  2J 
inches." 

The  cushion  coat  was  temporarily  abandoned  in  that  year.  The 
reason  for  this  is  instructive,  as  showing  the  defects  of  this  method 
of  construction.  Surfaces  laid  with  a  thickness  of  two  and  one- 
half  inches  the  lower  part  of  which  consisted  of  a  protective 
or  cushion  coat  richer  in  bitumen  were  liable  to  serious  displace- 
ment under  travel,  with  the  result  that  the  surface  became  very 
wavy  and  uncomfortable  to  drive  over,  an  experience  met  with  in 
other  cities  as  well,  and  which  subjected  such  asphalt  pavements 
to  unfavorable  comment.  The  excessive  thickness  and  the  richer 
cushion  coat  permitted  not  only  of  this  displacement  of  the  sur- 
face, but  also  allowed  its  movement  on  the  foundation  under 
the  impact  of  wheels  of  vehicles,  when  once  the  waves  were  formed, 
especially  where  travel,  as  in  streets  with  car-tracks,  was  confined 
in  one  direction. 

The  change  in  the  specifications  in  1886-87  was  intended  to 
avoid  this  by  doing  away  with  the  cushion  and  compacting  the 
entire  surface  at  once.  It  was  an  improvement,  but  for  some  reason 
the  provision  for  a  cushion  coat  one  or  two  per  cent  richer  in  asphalt 
appeared  again  in  the  specifications  for  1887-88.  No  asphalt 
pavements  were  laid  in  Washington  during  this  fiscal  year,  as  the 
city  was  compelled,  by  provisions  in  the  act  making  appropriations 
for  the  purpose,  not  to  go  beyond  a  limit  in  price  for  such  pavement 
for  which  the  contractors  refused  to  lay  asphalt.  A  return  was, 
therefore,  made  to  coal-tar  with  disastrous  results,  the  only  gain 


THE  INTERMEDIATE  COURSE.  21 

being  that  when  asphalt  surfaces  were  again  laid  in  1888  the  ex- 
cessive thickness  of  the  surface  was  reduced  and  a  course  of  broken 
stone  coated  with  coal-tar  or  asphalt  was  introduced  which  had 
been  an  element  of  the  so-called  distillate  pavements  of  the  inter- 
mediate period.  This  gain  was  a  distinct  one  for  the  asphalt- 
paving  industry  all  over  the  country,  as  it  did  away  with  the  dis- 
placement of  the  thicker  surface  under  traffic.  No  general  return 
to  the  original  method  of  construction  without  this  course  has  been 
made  since  that  time  except  in  two  or  three  cities,  and  there  with 
less  unsatisfactory  results  than  formerly  'owing  to  the  more  careful 
grading  of  the  mineral  aggregate  in  modern  mixtures  and  their 
greater  stability. 

The  Binder  Course. — The  binder  course,  as  has  been  said,  is 
an  inheritance  from  the  days  of  coal-tar  pavements  with  broken 
stone  foundations,  and  its  use  in  combination  with  an  asphalt  sur- 
face was  the  result  of  an  attempt  to  improve  upon  the  unsatis- 
factory distillate  pavement,  so  called,  laid  in  Washington  in  1887, 
by  substituting  an  asphalt  for  a  coal-tar  surface,  leaving  the 
foundation  and  binder  unchanged.  Eventually  a  hydraulic  con- 
crete foundation  was  substituted  for  the  broken  stone  and  the  re- 
sult was  the  modern  form  of  construction. 

The  binder  course  was  evidently  the  result  of  an  attempt  to 
close  the  large  openings  in  the  broken-stone  foundation  by  a  course 
of  finer  stone  in  order  to  prevent  the  loss  of  the  more  expensive 
surface  mixture  by  its  compression  into  the  voids  of  the  former 
and  with  no  idea  of  preventing  displacement  in  the  surface.  That 
it  accomplished  this  was  only  detected  when  it  was  noticed  that 
its  use  as  a  matter  of  economy  in  reducing  the  thickness  of  the 
asphalt  surface  from  two  and  one-half  to  one  and  one-half  inches 
produced  this  desired  result.  From  Washington  in  1888-89  the 
binder  course  rapidly  spread  over  the  country  and  proved  suc- 
cessful. In  its  original  form  it  consisted  of  "clean  broken  stone, 
thoroughly  screened,  not  exceeding  one  and  one-fourth  (1^)  inches 
in  the  largest  dimension  and  No.  4  coal-tar  paving  cement." 

The  coal-tar  was  soon  replaced  by  an  asphaltic  cement  and 
the  broken  stone  in  some  cities  by  a  smaller  stone  passing  an  inch 
ring  with  the  grit  and  finer  material  removed. 

From  a  binder   constructed  in  this  way  there  has  been  little 


22  THE  MODERN  ASPHALT  PAVEMENT. 

departure  for  many  years,  although  recently  the  possibility  of 
some  improvement  in  this  course  has  become  very  evident.  The 
original  course  was  one  and  one-half  inches  thick  when  compacted, 
a  depth  quite  necessary  with  one  and  one-fourth  inch  stone.  With 
finer  stone  and  for  economy  inch  binder  has  frequently  been  speci- 
fied, but  there  can  be  little  or  no  bond  to  such  a  thickness  and 
its  use  in  this  way  is  plainly  poor  practice. 

It  is  generally  specified  that  the  binder  stone  shall  pass  a  one 
and  one-fourth-  or  one-inch  screen  and  contain  not  more  than 
a  certain  percentage  of  fine  material.  This  is  a  great  mistake, 
as  in  the  case  of  hydraulic  concrete,  since  the  more  fine  material 
the  stone  contains,  up  to  the  point  where  the  voids  in  the  large 
particles  are  filled,  the  more  compact  and  desirable  the  binder  is. 
At  the  same  time  a  binder  with  much  fine  material  requires  a 
larger  amount  of  asphalt  cement  and  is  consequently  more  expen- 
sive. If  the  contractor  is  willing  to  assume  this  extra  expense 
no  objection  can  be  raised  to  such  a  practice. 

The  amount  of  asphalt  cement  necessary  to  coat  satisfactorily 
a  binder  of  clean  stone  free  from  grit  and  dust  will  vary  with  the 
character  of  the  stone  and  the  nature  of  the  asphalt  cement.  With 
Hudson  River  limestone  or  trap  three  per  cent  of  bitumen  is 
sufficient,  and  this  is  represented  by  that  amount  of  an  asphalt 
cement  composed  of  pure  bitumen  or  four  per  cent  of  one  made 
with  Trinidad  asphalt.  With  the  softer  limestones  of  the  middle 
West,  a  higher  percentage  is  occasionally  necessary.  The  exact 
amount  can  only  be  determined  by  experiment.  It  should  not  be 
sufficient  to  run  off  of  the  hot  stone  or  too  little  to  give  a  bright 
glossy  coat.  An  excess  may  result  disastrously,  as  it  will  collect 
inevitably  in  pools  or  spots  where  the  binder  has  been  taken  from 
the  bottom  of  the  truck  in  which  it  has  been  hauled  to  the  street, 
and  the  excess  collecting  at  these  points  may  be  drawn  up  by  a 
hot  summer  sun  and  soften  the  surface  of  the  pavement  or  even 
appear  in  mass  thereon,  as  has  happened  in  one  or  two  instances 
in  a  western  city. 

On  the  other  hand,  a  slight  and  well  distributed  excess  may 
prove  of  decided  benefit  on  streets  having  little  or  no  traffic,  where 
the  surface  would  be  apt  to  crack  ordinarily.  It  has  been  found 


THE  INTERMEDIATE  COURSE. 


23 


that  in  such  a  case  the  surface  is  slowly  enriched  by  the  excess, 
and  is  thus  preserved. 

An  example  of  this  enrichment  was  observed  in  an  Alcatraz 
surface  laid  on  a  very  rich  binder  in  a  western  city  in  1889.  A 
specimen  of  the  surface  was  analyzed  several  years  after  it  was 
laid,  after  separating  it  into  top  and  bottom  sections.  The  results 
were  as  follows : 


Section 

Bitu- 

Passim 

5  Mesh. 

men. 

200 

100 

80 

50 

40 

30 

20 

10 

Top  

9.8 

12.2 

10 

31 

32 

3 

1 

1 

0 

Duplicate. 

Bottom.  . 
Duplicate. 

9.8 

10.3 
10.7 

11.2 

11.7 
11.3 

10 

10 
10 

31 

32 
33 

33 

32 
31 

3 

2 

2 

1 

1 
1 

1 

1 
1 

0 

0 
0 

The  bottom  of  the  pavement  carries,  on  an  average,  seven-tenths 
per  cent  more  bitumen  than  the  top,  and  that  this  is  no  accident 
in  mixing  appears  from  the  uniformity  of  the  sand  grading  in 
all  the  samples  of  the  different  sections. 

The  consistency  of  the  asphalt  cement  hi  use  in  binder  should 
be  softer  than  that  in  the  surface  for  several  reasons.  The  ordinary 
binder  is  a  very  open  material  which  permits  the  volatilization  of 
oil  from  the  asphalt  cement  by  the  heat  of  the  stone,  especially 
if  the  stone  is  accidentally  too  hot  and  the  haul  to  the  work  a 
long  one,  with  the  result  that  the  cement  becomes  much  hardened 
and  more  brittle.  In  the  second  place  the  tendency  to  the  rupture 
of  the  bond  between  the  fragments  of  binder  stone  is  much  less 
with  an  asphalt  cement  of  soft  than  of  hard  consistency. 

Good  practice  leads  to  the  use  of  a  cement  for  binder  which 
is  twenty  or  more  points  softer,  by  the  penetration  machine, 
than  that  hi  the  surface. 

The  actual  temperature  of  the  binder  as  it  is  laid  on  the  street 
should  be  no  greater  than  is  necessary  to  make  it  possible  to.  rake 
it  out.  It  may  be  much  colder  than  an  asphalt  surface  mixture. 

Recent  experience  has  shown  that  there  are  defects  in  such 
a  binder  which  are  due  to  the  fact  that  the  voids  are  unfilled  and 


24 


THE  MODERN  ASPHALT  PAVEMENT. 


the  course  lacks  stability  and  solidity.  Such  defects  have  been 
manifested  in  two  ways  for  many  years.  If  binder  is  not  laid  with 
great  attention  to  the  character  of  the  asphalt  cement  which  covers 
the  stone  and  binds  it  together  it  soon  loses  its  bond  under  heavy 
traffic  and,  the  stone  itself  having  but  little  supporting  power, 
the  asphalt  surface  goes  to  pieces.  If,  on  the  other  hand,  the 
binder  stone  itself  is  not  a  strong  one  it  is  frequently  crushed  by 
the  weight  of  heavy  traffic  and  the  surface,  losing  its  support, 
either  goes  to  pieces  or  the  crushed  binder  is  forced  into  it  irregu- 
larly, thus  causing  a  decided  displacement  which  eventually  results 
in  disintegration. 

In  individual  cases  the  surface  has  been  observed  to  have  been 
driven  by  traffic  into  the  voids  in  the  binder  without  displacement, 
with  the  result  that  the  thickness  of  the  pavement  has  been  much 
reduced,  although  in  this  condition  it  is  a  much  more  rigid  mass 
than  as  it  was  first  constructed. 

The  binder  previously  described  has  consisted  of  stone  prac- 
tically or  largely  of  one  size,  three-quarters  to  one  and  one-half 
inches  in  the  largest  diameter,  as  appears  from  the  following  an- 
alyses: 


Test  number  .... 

69978 

70804 

70854 

71102 

74893 

Bitumen     .  . 

54% 

44% 

3.8% 

36% 

3.5% 

Filler     

4  IT 

2.21    n~ 

2.4  1     KA 

1.5  |    ,  e 

Sand    

21  o  r^-8 

12]5  )  16'6 

7.5J    9'7 

3.0  /    5A 

3.0  r  4-5 

Stone: 

Passing  \"  sieve 

5.81 
13.6    67  8 

8.71 
46.8     79Q 

18.0] 
52.0  )  86  5 

13.51 
51.5  L10 

49.51 

10.0  L20 

1"     " 

41.4  F67-8 

23.5  ['  y'U 

16.5  j 

26.0  f  y  >u 

32.5  j 

Retained  1"  " 

7.0  J 

0.0  J 

0.0  J 

0.0  J 

0.0  J 

100.0 

100.0 

100.0 

100.0 

100.0 

It  will  be  seen  from  the  preceding  results  that  the  percentage 
of  bitumen  which  binder  will  carry  depends  largely  upon  the 
amount  of  fine  material  which  it  contains,  binder  No.  69978  with 
26.8  per  cent  of  fine  material  holding  5.4  per  cent  of  bitumen,  while 
those  made  from  cleaner  stone  where  the  fine  material  does  not 
exceed  5  per  cent,  carry  less  than  4  per  cent  of  bitumen.  If  the 


THE   INTERMEDIATE    COURSE.  25 

stone  in  use  is  not  screened,  but  contains  all  the  finer  particles 
coming  from  the  crusher,  the  binder  will  be  more  satisfactory. 

Asphaltic  Concrete  Binder. — The  weakness  of  the  ordinary 
open-binder  course,  where  subjected  to  heavy  traffic,  can  be 
avoided  by  filling  the  voids  in  the  material  with  fine  stone  or  grit 
and  the  remaining  voids,  after  this  addition,  with  sand  or  a  mineral 
aggregate  corresponding  in  grading  to  that  of  a  standard  surface 
mixture. 

Such  a  binder  has  given  most  excellent  results  in  supporting 
an  asphalt  surface  on  an  ordinary  foundation,  such  as  turned  or 
reset  blocks  or  alongside  of  poorly  constructed  street-railway 
tracks,  such  as  those  on  Broadway  in  New  York  City,  being  hi 
itself  perfectly  rigid. 

A  good  example  of  this  form  of  construction  on  a  hydraulic 
concrete  foundation  may  be  seen  on  Court  Street  in  Boston,  from 
Washington  Street  to  the  old  Court  House,  and  on  Kilby  Street 
in  the  same  city,  between  State  and  Central  Streets.  A  photograph 
of  a  sawn  section  of  such  pavement  is  shown  in  Fig.  16. 

The  manner  in  which  a  binder  of  this  type,  which  is  generally 
known  hi  the  industry  as  close  or  compact  binder,  is  turned  out  at 
the  plant  is  much  the  same  as  that  used  in  preparing  an  as- 
phaltic  concrete  to  be  used  as  a  wearing  surface,  with  the  exception 
that  it  contains  no  filler,. and  will  be  described  in  a  later  chap- 
ter. It  will  be  of  interest,  however,  to  give  some  examples  of  the 
proportions  in  which  the  various  components  have  been  employed 
in  actual  practice  during  the  year  1907,  together  with  the  results 
of  analyses  of  the  finished  binder.  (See  Table  on  page  26.) 

Close  binder  of  the  Boston  type  is  probably  more  desirable  than 
that  produced  in  New  York,  owing  to  the  larger  percentage  of 
three-quarter  inch  stone  which  it  contains  and  its  consequent 
greater  stability,  but  as  the  stone  at  that  point  is  not  separated 
into  two  sizes  after  heating,  but  drawn  from  one  bin,  there  is 
probably  a  greater  amount  of  segregation  in  the  mixture  than  in 
that  turned  out  at  New  York,  where  stone  of  each  size  is  separated 
and  weighed  out  in  definite  proportions.  Nevertheless,  a  very 
satisfactory  asphaltic  concrete  for  the  binder  course  has  been 
turned  out  in  Boston  in  that  way,  with  the  exception  that  where 


26 


THE    MODERN    ASPHALT    PAVEMENT. 


New  York. 

Boston. 

Plant  1. 

Plant  2. 

Coarse  stone 

480  lbs.  =  54.6% 
200    u       22.7 
150   "       17.0 

50   "         5.7 

480  lbs.  =  53.3% 
202    "       22.4 
150    "       16.7 
68    "        7.6 

}  885  Ibs.  =73.4% 

250  "       20.8 
70  "        5.8 

Fine  stone       

Sand                      

Trinidad  asphalt  cement 
Bermudez 

880  Ibs.  100.0 

900  Ibs.  100.0 

1205  Ibs.  100.0 

ANALYSES: 


Bitumen  soluble  in  CSS. 
Passing  200  mesh  screen 

5,% 

5.2% 
6.4 

4.8% 
4.2 

'          10     "         " 

29.2 

29.0 

26.4 

*      "         " 

1.8 

2.0 

.8 

i  inch 

10.0 

7.0 

4.4 

«                l      if,             rt 

23.2 

25.8 

24.4 

t                    3       «                 tl 

13.6 

17.8 

32.2 

t                     «            n 

7.4 

6.8 

2.8 

Retained   1    " 

4.8 

0.0 

0.0 

100.0 

100.0 

100.0 

there  is  segregation  of  the  finer  material,  it  sometimes  happens 
that  there  will  be  a  displacement  of  the  surface  of  the  finished 
pavement  at  that  point. 

On  this  account,  there  are  one  or  two  points  which  experience 
has  shown  must  be  guarded  against.  The  fine  material  should 
not  be  at  all  in  excess  of  an  amount  sufficient  to  fill  the  voids  in 
the  stone,  since,  if  this  is  the  case,  too  smooth  a  surface  will  be 
obtained,  with  resulting  displacement  of  the  wearing  surface.  An 
excess  of  bitumen  must  also  be  avoided  for  the  same  reason. 

In  the  construction  of  an  asphalt  pavement  with  an  asphaltic 
concrete  binder  course,  the  surface  should  be  applied  to  the  binder 
before  it  has  become  entirely  cold,  in  order  to  obtain  a  satisfactory 
bond.  It  is  not  possible  to  do  satisfactory  work  where  a  large  area 
of  close  binder  is  laid  on  one  day  and  covered  with  surface  on  the 
next.  There  should  be  an  alternation  of  the  binder  and  surface 
courses,,  for  example,  no  more  binder  should  be  laid  in  the  begin- 


THE  INTERMEDIATE   COURSE.  27 

ning  of  a  day  than  can  be  covered  with  surface  during  the  remain- 
der of  the  available  working  hours. 

Where  old  surface  mixture  is  available  and  facilities  are  at 
hand  for  softening  this  by  means  of  heat  or  by  grinding  it  in  a 
disintegrator,  such  material  can  be  used  quite  as  satisfactorily 
for  filling  the  voids  in  an  ordinary  binder  as  new  sand  and  filler, 
thus  reducing  very  much  the  cost  of  a  concrete  binder  course. 
The  percentage  of  asphalt  and  its  consistency  in  such  a  case  will, 
of  course,  be  regulated  by  the  amount  already  present  in  the  old 
material. 

The  form  of  construction  involving  the  use  of  a  compact  binder 
naturally  increases  the  cost  of  the  pavement  to  a  certain  extent, 
but  the  advantages  gained  more  than  make  up  for  this,  since  its 
life  will  be  extended  to  a  degree  more  than  sufficient  to  bring  the 
cost  per  year  below  that  of  one  in  which  the  old  open  form  of  binder 
is  used,  especially  on  streets  of  heavy  travel.  In  the  author's 
opinion  it  is  the  most  important  advance  that  has  been  made  in 
the  asphalt  paving  industry  since  the  evolution  of  the  rationally 
graded  surface  mixture  in  1896.  Its  use  is  specified  in  Kansas 
City  and  Omaha,  as  can  be  seen  in  the  very  excellent  specifications 
of  the  former  city,  which  are  reprinted  in  the  appendix. 

Paint-coat. — Some  of  the  defects  in  a  pavement  due  to  an 
open  binder  can,  perhaps,  also  be  removed  by  abandoning  it  entirely 
and  substituting  therefor  a  so-called  paint  course  which  con- 
sists of  an  asphalt  cement  of  suitable  consistency  dissolved  in 
benzine,  62°  B.,  and  then  applied  with  a  brush  or  squeegee  to  the 
surface  of  the  hydraulic  foundation,  which  should  be  made,  if  this 
coat  is  used,  of  Portland  cement,  or  else  floated  with  a  mortar  of 
this  cement,  and  should  have  a  comparatively  smooth  surface. 
The  coating  should  be  bright  and  glossy,  but  not  sticky,  and  it 
must  be  carefully  protected  from  becoming  dirty.  It  cannot 
be  applied  successfully  to  a  concrete  that  is  in  the  slightest  degree 
damp,  as  the  adhesion  is  then  imperfect.  If  well  done,  and  this 
requires  some  skill  and  experience,  the  surface  mixture  applied 
directly  to  this  coat  will  be  cemented  firmly  to  it  and  any  displace- 
ment in  the  surface  on  the  foundation  will  be  prevented  if  the 
mixture  itself  is  stable. 


28  THE  MODERN  ASPHALT  PAVEMENT. 

The  first  use  of  such  a  coat  as  a  substitute  for  binder  was  made 
in  a  town  in  Ohio  in  1896,  where  an  asphalt  surface  was  laid  on 
an  old  brick  pavement,  the  grade  of  which  did  not  permit  of  the 
use  of  a  binder  course.  The  adhesion  of  the  surface  to  the  brick 
was  afterwards  found,  on  making  cuts  for  water  and  gas  connec- 
tions, to  be  so  strong  that  the  upper  portions  of  the  brick  were 
torn  away  with  the  asphalt  surface.  On  one  or  two  streets  in 
New  York  on  which  very  heavy  coal  trucks  are  constantly  passing, 
and  where  the  binder  course  was  frequently  crushed,  a  similar 
construction  on  a  Portland-cement  base  was  successful. 

Specifications  for  the  use  of  paint  coat  are  as  follows: 
"Upon  the  surface  of  the  foundation  of  the  Portland  cement 
concrete,  a  paint  course  shall  be  applied  to  bind  or  tie  the  surface 
course  to  the  foundation.  For  this  purpose,  the  surface  of  the 
cement  concrete  shall,  in  its  preparation,  be  well  rammed,  so  that 
mortar  shall  come  to  the  top,  and  it  shall  be  made  so  smooth  that 
no  depression  shall  exist  of  a  depth  of  more  than  three-eighths  (f ) 
of  an  inch.  The  paint  for  use  shall  consist  of  62°  B.  naphtha  and 
any  satisfactory  asphalt  cement  free  from  mineral  matter,  and 
of  a  consistency  such  as  will  allow  the  penetration,  at  77  degrees 
Fahrenheit,  of  a  No.  2  needle  weighted  with  100  grams,  of  not 
more  than  three  (3)  millimeters,  and  not  less  than  two  (2). 
The  asphalt  cement  shall  be  dissolved  while  soft  and  warm,  in  the 
naphtha  in  such  proportions  that  the  resulting  paint  shall  give  a 
glossy  surface  after  evaporation  of  the  latter,  but  at  the  same 
time  can  be  applied  so  as  to  form  as  thin  a  coating  as  possible. 
The  proportions  will  vary,  depending  upon  the  temperature  at 
which  the  paint  is  made,  but  shall  be  about  240  pounds  of  asphalt 
cement  to  50  gallons,  or  one  barrel,  of  naphtha, 

"The  concrete  foundation  shall  be  carefully  swept  and  thorough- 
ly cleaned  of  all  foreign  matter.  The  paint  coat  shall  only  be 
applied  to  it  when  the  latter  is  absolutely  dry  and  free  from  the 
slightest  dampness,  as  otherwise  it  will  not  adhere.  It  should  be 
used  in  such  quantity  that  fifty  (50)  gallons  will  cover  from  350 
to  4QO  square  yards  of  the  concrete  surface. 

"No  more  of  the  surface  of  the  foundation  shall  be  painted  than 
can  be  covered  with  asphalt  surface  mixture  within  a  few  hours  after 


THE  INTERMEDIATE   COURSE.  29 

the  application.  Under  no  circumstances  shall  the  paint  coat  be 
allowed  to  become  in  any  way  dirty,  nor  shall  the  surface  mixture 
be  permitted  to  be  applied  to  such  a  coat  more  than  five  hours  after 
the  painting  has  been  done. 

"Owing  to  the  inflammability  of  naphtha,  the  paint  shall  be 
prepared  at  a  distance  from  all  fire  or  flame  and  shall  be  applied  to 
the  surface  of  the  concrete  with  the  same  precautions." 

SUMMARY. 

In  the  preceding  chapter  it  appears  that  the  use  of  a  so-called 
cushion  coat — that  is  to  say,  the  application  of  the  surface  mixture 
to  the  foundation  in  two  courses  instead  of  one — is  usually  unsat- 
isfactory and  has  generally  been  abandoned.  The  ordinary  open- 
binder  course  has  been  shown  to  be  defective,  owing  to  its  lack  of 
stability,  on  heavy-traffic  streets  and  the  substitution  for  it  of  a 
compact  binder  has  been  recommended,  or,  where  economy  is 
desired,  the  use  of  a  paint-coat  to  tie  the  surface  mixture  to  the 
foundation. 

An  open  binder  course  of  this  description  will  no  doubt  con- 
tinue to  be  very  generally  an  element  in  the  construction  of  the 
majority  of  asphalt  pavements  which  are  subjected  to  only  mod- 
erate traffic. 


PART  II. 

THE    MATERIALS    CONSTITUTING    THE    ASPHALT 
SURFACE  MIXTURE. 


CHAPTER  III. 
THE  MINERAL  AGGREGATE. 

THE  asphalt  surface,  which  directly  carries  the  traffic  and 
which  is  intended  to  withstand  the  wear  and  tear  of  the  same  and 
the  action  of  the  elements,  is  composed  of  a  mineral  aggregate 
and  an  asphalt  cement,  that  is  to  say,  it  is  an  asphalt  mortar 
or  concrete. 

The  mineral  aggregate  consists  of  sand,  in  exceptional  cases 
also  of  stone,  and  a  fine  mineral  dust  or  filler. 

The  asphalt  cement  consists  of  a  native  hard  asphalt,  or  some 
hard  residue  from  an  asphaltic  oil  or  maltha,  softened  to  the 
proper  consistency  by  some  heavy  petroleum  oil,  generally  the 
residual  product  of  the  distillation  of  petroleum. 

Before  considering  surface  mixture  as  a  whole  the  constituents 
which  enter  into  its  composition  must  be  examined  individually 
and  the  variations  which  are  met  with  in  them  noted. 

The  Mineral  Aggregate. — Sand  — Sand  is  the  detritus  of  rock, 
consisting  of  particles  smaller  than  gravel  and  larger  than  silt, 
and  produced  either  by  natural  causes  such  as  weathering  and 
water  action  or  by  the  hand  of  man  in  crushing  rocks  mechanically. 

Natural  sand  is  the  detritus,  generally,  of  crystalline  rocks 

30 


THE  MINERAL  AGGREGATE.  31 

and  commonly  water  borne  and  water  worn,  in  which  quartz 
usually  predominates,  although  calcareous  sands,  and  those  com- 
posed entirely  of  feldspar  or  largely  of  other  silicates,  are  known. 

Artificial  sand  consists  of  the  particles,  produced  in  the  process 
of  crushing  rocks,  which  are  of  corresponding  size  to  those  which 
make  up  natural  sands. 

Sand  is  the  principal  constituent  of  asphalt  pavements,  and 
as  such  demands  careful  attention  and  study.  Mr.  A.  W.  Dow  has 
remarked  in  a  paper  before  the  Society  of  Municipal  Improvements 
in  1898: 

"As  sand  is  90  per  cent  of  the  pavement,  why  should  it  not 
be  the  most  important  ingredient  to  consider;  and  when  a  pave- 
ment is  at  fault,  why  should  it  not  be  more  responsible  than  the 
asphalt  which  now  bears  the  brunt  of  all  failures?" 

As  a  matter  of  fact  it  is  now  pretty  well  known  that,  even 
if  all  the  other  constituents  of  an  asphalt  surface  mixture  are 
of  the  best,  the  wearing  surface  will  not  prove  a  success  unless 
the  sand  is  suitable  for  the  purpose. 

In  the  early  days  of  the  asphalt-paving  industry  but  little 
attention  was  given  to  the  subject  and  the  sand  hi  use  was  what- 
ever happened  to  be  the  most  available  at  the  particular  locality 
where  work  was  being  done.  Later,  opinions  varied  as  to  whether 
a  coarse  or  a  fine  sand  was  more  desirable,  and  there  was  a  vibration 
from  one  to  the  other,  together  with  equally  wide  variations  in 
the  consistency  of  the  asphalt  cement.  In  1890  we  find  an  expert 
of  that  day  stating  that  he  is  "pretty  well  convinced  that  sand 
and  matter  that  passes  the  60  mesh  ought  not  to  enter  the  mix- 
ture"; and  again  in  1892,  having  examined  "ten  old  pavements 
that  have  withstood  wear,"  saying:  "taking  these  results  [of  his 
analyses]  on  the  face  of  it,  it  is  observed  that  in  general  the  sand 
used  was  on  the  fine  side."  No  definite  conclusions  were  drawn 
at  that  time  as  to  what  a  desirable  sand  was. 

To-day  we  are  better  informed  as  to  the  best  sand  for  a  good 
surface  mixture,  but  unfortunately  we  know  too  little  in  regard 
to  the  cause  of  the  varying  character  of  the  particles  composing 
the  quartz  sand  which  is  used.  We  have  not  been  able  to  tell 
why  a  certain  Missouri  River  sand  produces  such  a  mushy  mixture 


32  THE  MODERN  ASPHALT  PAVEMENT. 

and  is  so  unsatisfactory  that  its  use  has  had  to  be  abandoned,  or 
why  a  Platte  River  sand  is  possessed  of  peculiarities  seen  in  that 
from  no  other  river. 

Difference  in  the  shape  of  the  grain  and  in  the  character  of 
its  surface  are  the  probable  causes,  and  these  characteristics  of 
a  sand  are,  therefore,  probably  next  in  importance  to  the  composi- 
tion and  size  of  the  grains  in  determining  its  suitability  for  paving 
purposes. 

Sorby,1  who  has  studied  the  subject  of  sands  carefully,  has 
classified  them  as  follows: 

"  1.  Normal,  angular,  fresh-formed  sand,  such  as  has  been 
derived  almost  directly  from  the  breaking  up  of  granite  or  schistose 
rocks. 

"  2.  Well-worn  sand  in  rounded  grams,  the  original  angles  being 
completely  lost  and  the  surfaces  looking  like  fine-ground  glass. 

"  3.  Sand  mechanically  broken  into  sharp  angular  chips,  show- 
ing a  glassy  fracture. 

"  4.  Sand  having  the  grains  chemically  corroded,  so  as  to  pro- 
duce a  peculiar  texture  of  the  surface,  differing  from  that  of  worn 
grains  or  crystals. 

"  5.  Sand  in  which  the  grains  have  perfectly  crystalline  outline, 
in  some  cases  undoubtedly  due  to  the  deposition  of  quartz  upon 
rounded  or  angular  nuclei  of  ordinary  non-crystalline  sand." 

In  the  paving  industry  all  these  sands  have  been  met  with, 
but  grains  of  several  kinds  not  mentioned  by  Sorby  are  frequently 
found.  From  an  examination  of  several  hundred  sands  from  dif- 
ferent localities  the  writer  has  been  able  to  classify  them,  according 
to  their  source,  by  peculiarities  of  composition,  by  the  shape,  and 
by  the  surface  of  the  grains,  as  follows: 

Classification  of  Sand. 
Source: 

Commercially. 
1.  Beach  sand. 
Seashore. 
Lakeshore. 

»Q.  J.  GeoL  Soc.,  1880,  36,  58. 


THE    MINERAL    AGGREGATE.  33 

2.  River  sand. 

3.  Bank  sand. 

4.  Sand  derived  from  soft  sandstone. 

5.  Artificial  sand. 

Or  with  especial  reference  to  their  physical  origin. 

1.  Beach  sand. 

Marine — tidal  action  and  sorting. 
Lakeshore — storm  action  and  sorting. 

2.  Alluvial  sand. 

Subaqueous,  recent. 

Stream. 

Lake. 

Bank  or  pit  deposits. 
Glacial,  stream,  lake,  etc. 

3.  ^Eolian  sand. 

Dune. 


Volcanic. 

4.  From  sandstone. 

5.  Crushed  stone. 

Composition: 

Silica. 
Quartz. 
Hard  clear. 
Soft  cloudy. 
Ferruginous. 
Silicates. 

Shales  and  schists. 
Feldspar. 

Hornblende,  Pyroxenes. 
Calcareous. 

Limestone. 
Carbonates. 
Shell. 
Coral. 


34  THE  MODERN  ASPHALT  PAVEMENT. 

Mixed  composition. 

Various  kinds  of  quartz. 
Quartz  and  silicates. 
Quartz  and  carbonates. 
Quartz  and  shell. 

Shape: 

Irregular. 

Sharp  angles. 

Rounded  angles. 
Oval. 

Worn  by  water  action. 
Round. 

River. 

Glacial. 

Rock. 
Crystalline. 

Surface : 

Sharp,  original  or  fractured  surface,  not  at  all  or  little 

worn. 

Slightly  worn  on  edges. 
Smooth  and  polished  "soft  sand." 
Smooth  and  with  surface  like  ground  glass. 
Covered  with  cementing  material. 
Acted  upon  chemically. 
Porous,  coral  sand,  limestone  sand,  shells. 

Size  of  grains : 
Uniform. 

Particles  distributed  in  size,  well  graded. 
Quicksand. 

These  different  classes  of  sand  may  be  described  with  special 
reference  to  their  use  in  the  asphalt  industry. 

Beach  Sands. — Seashore. — These  are  little  used  because  as  a 
rule  they  are  so  sorted  by  currents  of  more  or  less  uniform  hydraulic 
value  that  they  are  too  much  of  one  size.  For  example,  a  sand 
found  on  Rockaway  Beach,  Long  Island,  is  made  up  of  grains 
passing  the  following  sieves: 


THE    MINERAL    AGGREGATE.  35 

Passing  200-mesh  sieve 0% 

100-    "         "    7 

80-    "         "    32 

50-    "         "    57 

40-    "         "    2 

30-    "         ".    1 

"         20-    "         "    1 

"         10-    "         "    0 

100 


It  appears  that  89  per  cent  of  all  the  particles  in  the  sand  are 
of  50-  and  80-mesh  size.  The  tidal  currents  are  such  that  par- 
ticles of  smaller  size  are  washed  away  while  the  larger  ones 
have  been  left  behind  in  the  movement  of  the  beach  sand  to  its 
present  location. 

As  far  as  character  of  the  grain  is  concerned  beach  sands  often, 
and  in  fact  in  most  cases,  could  not  be  improved  upon.  Fig.  2, 
No.  1. 

The  most  remarkable  seabeach  sands  in  the  United  States 
are  found  on  the  eastern  coast  of  Florida.  They  consist,  on  the 
beaches  of  the  northern  part  of  the  State,  of  pure  white  quartz 
grains  which  have  a  fresh  and  angular  fracture.  Further  south, 
as  at  Lake  Worth  Inlet,  they  are  made  up  of  quartz  and  shell 
fragments  of  about  the  same  size.  The  grains  are  much  coarser 
owing  to  local  conditions.  Fig.  2,  No.  2. 

An  explanation  of  the  presence  of  quartz  sand  at  a  point  so 
far  distant  from  any  rock  formations  which  contain  this  material 
can  only  be  arrived  at  by  assuming  that  this  mass  of  sand  has 
been  transported  down  the  coast  by  tidal  action  and  ocean  currents. 


No.  30516— Lake  Worth  Inlet;  bar  sand;  about  6  miles  from  Palm  Beach, 

Florida. 

"    30534 — St.  Augustine;  north  beach;  from  dunes  10  to  15  feet  high. 
' '    30535 —  "  "  "         ' '       along  high-water  line ;  river  side. 

"    30536—"          "  "         "          "  "  "      ocean  side. 

"    30547— St.  John's  Bluff. 
"    30546 — Mayport,  Duval  County;  from  1  mile  south  of  Mayport,  \  mile 

from  ocean. 
"    30548 — Mayport,  Duval  County;  from  sand-dunes  10  feet  high. 


36 


THE  MODERN  ASPHALT  PAVEMENT. 


Test  number  

30516 

30534 

30535 

30536 

30547 

30546 

30548 

Passing   200-mesh 

0% 

1% 

1% 

1% 

1% 

2% 

1% 

100- 

1 

45 

31 

32 

18 

6 

39 

80- 

1 

41 

50 

50 

39 

20 

50 

50- 

16 

12 

17 

16 

26 

39 

9 

40- 

40 

1 

1 

1 

10 

19 

1 

30- 

22 

0 

0 

0 

2 

8 

0 

20- 

15 

0 

0 

0 

2 

4 

0 

10- 

5 

0 

0 

0 

2 

2 

0 

100 

100 

100 

100 

100 

100 

100 

T3rk4-0!r^«J      -|  f\          <( 

AC/ 

1     1  C7 

2    no/ 

xvetaineQ  lu- 

.4y(- 



> 

l.l/p 

•U/o 

^rklnHlo  in   TTP1 

Ar    QO7 

1K.C7 

2707 

QO7 

1     9O7 

ooiuDie  in  xiui.  .  . 

•*O  .  \J  /o 

•b/o- 

•  •  /o 

•o  /O 

1-^/0 

The  above  sands  are  all  pure  quartz  with  the  exception  of 
sample  No.  30516  from  Lake  Worth  Inlet,  which  contains  45.9 
per  cent  shell  detritus. 

The  beach  sands  of  Cuba,  to  the  west  of  Havana,  are  composed 
entirely  of  small  shell  fragments,  while  those  on  the  south  coast 
to  the  east  of  Santiago  are  either  coral  or,  in  Daiquiri  Bay,  largely 
of  hard  silicates,  the  particles  being  transparent  and  of  the  rich 
color  of  hornblende. 

Seabeach  sands  are  reputed  to  be  far  from  sharp,  but  among 
many  recently  examined  for  their  suitability  for  use  in  the  paving 
industry  most  of  them  have  proved  sharper  than  river  or  bank 
sand.  Fig.  2,  No.  1. 

Beach  Sands.  —  Lakeshore. —  Another  form  of  beach  sand  is 
found  on  the  shores  of  the  numerous  lakes  near  some  of  our  large 
cities,  the  great  lakes  in  the  North,  and  Lake  Pontchartrain  in 
the  South. 

The  assorting  of  the  particles  composing  lakeshore  sands  is 
accomplished  largely  by  the  movement  of  water  produced  by 
storms,  a  more  complicated  one  usually  than  is  presented  on  the 
seabeaches,  although  not  as  powerful  as  a  rule.  Tidal  action  is 
of  course  absent.  In  many  localities  the  force  of  the  waves  or 
of  the  induced  currents  are  so  small  as  to  permit  of  the  deposition 
of  very  fine  sand  or  of  that  in  which  the  particles  are  very  well 
graded  in  size.  In  other  cases  there  is  a  great  similarity  between 
lake  and  seabeach  sands.  The  remarkable  variation  in  the  size 


FIG.  2. — Sand  Grains- 


38 


THE  MODERN  ASPHALT  PAVEMENT. 


of  lakebeach   sand,  even  on  beaches  within  a  few  miles  of  each 
other,  is  illustrated  by  the  following  examples: 


Lake  Michigan. 

Lake  Erie. 

Kenosha,  Wis. 
1899. 

Chicago,  111. 
1897. 

Sandusky, 
Ohio. 

Pas 

sing  200-me 
100- 
80- 
50- 
40- 
30- 
20- 
10- 

'sh  sie 
t 

ve 
t 

2% 

16 
52 
13 
3 
2 
4 

100 

10% 
68 
15 
3 
3 
1 
0 
0 

100 

o% 
11 

23 
24 
32 

7 
2 
1 

100 

In  the  Kenosha  sand,  although  the  uniformity  of  grade  is  not 
carried  as  far  as  was  the  case  on  Rockaway  Beach,  52  per  cent 
of  the  particles  are  of  a  size  to  pass  a  sieve  of  50  meshes  to  the 
inch.  And,  again,  we  have  finer  sand  from  near  Chicago  of  still 
greater  uniformity.  On  the  other  hand,  near  Sandusky  a  lake 
sand  is  available  which  is  of  quite  varied  size  of  grains.  Here  the 
sorting  of  the  sand  particles  has  been  limited  and  the  grading 
is  satisfactory  for  use  in  asphalt  surface  mixtures  without  modi- 
fication. Where  lake  sands  are  of  too  uniform  size  two  or  more 
sources  of  supply  may  be  used  and  mixed  in  suitable  proportions. 
Other  typical  beach  sands  from  Lakes  Michigan,  Erie,  and  Ontario, 
which  are  in  the  writers'  collection,  sift  as  follows : 


Milwaukee 
Beach. 

White  Fish 
Bay,  Wis. 

Lake 
Ontario. 
1894. 

Lake 
Pontchar- 
train. 

Lake  Erie. 

1892. 

Passing  200-mesh.      .  . 

o% 

1% 

1% 

0% 

2%. 

100-          .      .  . 

2 

27 

2 

0 

29 

80-          ... 

6 

32 

46 

1 

14 

50-          ... 

32 

32 

44 

28 

47 

40-          ... 

22 

3 

3 

47 

4 

30-          ... 

14 

2 

2 

21 

2 

20-          ... 

14 

0 

1 

3 

2 

10-          .      .. 

10 

3 

1 

0 

0 

100 

100 

100 

100 

100 

THE    MINERAL    AGGREGATE.  39 

The  very  considerable  variations  in  the  size  of  these  sands 
from  different  sources  make  it  possible,  however,  by  mixing  those 
of  different  sizes,  to  produce  a  sand  of  any  grading  that  may  be 
desired  for  a  surface  mixture,  and  that,  too,  without  great  labor. 

A  peculiarity  of  lakebeach  sand  is  the  rapidity  with  which 
all  the  sand,  which  may  be  of  most  desirable  character  for  asphalt 
work,  may  be  removed  from  any  particular  locality  by  a  violent 
winter  storm  and  its  place  taken  by  a  sand  of  quite  different  grad- 
ing. This  is  of  common  occurrence  between  Chicago  and  Mil- 
waukee, and  no  doubt  elsewhere,  so  that  the  fact  that  a  suitable 
sand  can  be  found  at  a  particular  point  during  any  one  working 
year  does  not  mean  that  the  sand  will  be  of  the  same  grading 
another  year,  especially  if  the  storms  of  an  intervening  winter 
have  been  heavy.  The  variation  in  the  available  sand  from  year 
to  year  in  this  way  makes  a  decided  difference  in  the  character 
of  the  asphalt  mixture  turned  out  at  different  times  in  cities  which 
are  dependent  on  such  a  source  of  supply. 

Lakebeach  sands,  originating  at  old  lake  levels,  may,  like 
alluvial  sands,  be  found  at  times  in  banks  or  pits  where  changes 
of  lake  levels,  which  are  so  frequent  in  geological  time,  have  left 
them  above  the  elevation  of,  and  at  times  far  distant  from,  the 
present  water  level.  For  commercial  uses  these  cannot  be  dis- 
tinguished from  beach  sands  of  more  recent  origin. 

Alluvial  Sands  include  all  those  which  have  been  moved  by 
and  deposited  from  running  water  as  distinguished  from  beach 
sands.  They  may  be  found  to-day  in  the  beds  of  streams  or  along 
their  shores  and  in  banks  and  pits  where  they  have  been  left  by 
running  water  in  past  geological  times.  Alluvial  sands  may 
also  include  those  originating  in  glacial  streams  and  occurring 
both  in  banks  and  pits  and  as  reassorted  by  recent  water  action. 
There  are  also  deposits  in  lakes  from  streams  flowing  into  them 
which  need  not  enter  into  our  consideration,  being  rarely  so  avail- 
able as  to  be  of  technical  importance. 

River  Sands.  —  As  river  sands  are  conveniently  considered 
those  which  are  found  in  the  beds  of  streams  or  on  their  beaches, 
and  which  are  still  largely  subject  to  the  action  of  water.  They 
are  oftener  found  at  the  concave  side  of  some  bend  or  at  a  place 


40  THE  MODERN  ASPHALT  PAVEMENT. 

where  the  current  makes  a  change  in  direction  or  loses  its  force. 
Geikie  describes  the  deposition  of  river  sand  as  follows: 

"While  the  main  upper  current  is  making  a  more  rapid  sweep 
round  tho  opposite  bank,  under  currents  pass  across  to  the  inner 
side  of  the  curve  and  drop  their  freight  of  loose  detritus,  which, 
when  laid  bare  in  dry  weather,  forms  the  familiar  sand-bank  or 
shingle-beach.  Again,  when  a  river  well  supplied  with  sediment 
leaves  mountainous  ground  where  its  course  has  been  rapid  and 
enters  a  region  of  level  plain,  it  begins  to  drop  its  burden  on  the 
channel." 

feiver  sands  are  usually  obtained  by  dredging  and  are  thus 
distinguished  from  bank  or  pit  sand,  which  are  worked  from  dry 
deposits.  They  are  most  varied  in  character  and  form  an  impor- 
tant part  of  the  supply  in  use  in  asphalt  paving.  In  each  river 
they  seem  to  have  distinguishing  peculiarities,  and  in  no  two  cities 
having  their  source  of  sand  in  a  river  bottom  is  the  supply  of 
the  same  character,  while  for  any  one  city  the  supply  may  vary 
in  character  from  year  to  year. 

This  may  be  due  to  two  causes :  to  the  different  nature  of  the 
rock  formations  from  which  the  sand  found  in  different  rivers 
is  derived  and  to  the  different  physical  conditions  to  which  the 
debris  from  these  formations  has  been  exposed,  resulting  in  pecu- 
liarities of  shape,  size,  surface,  etc. 

River  Sand  at  Kansas  City  and  Washington,  D.  C.,  etc. — River 
sands  are  or  have  been  in  use  in  Washington  from  the  Potomac,  in 
Kansas  City  from  the  Missouri  and  from  the  Kansas,  in  Omaha 
from  the  Platte,  and  in  St.  Louis  from  the  Mississippi  and  Missouri. 
No  two  of  the  sands  resemble  each  other  in  their  behavior  in  an 
asphalt  surface  mixture.  The  peculiarities  which  each  one  shows 
can  be  described,  but  as  yet  it  is  impossible  to  show  why  they 
all  differ  so  much  in  their  adaptability  to  making  a  desirable 
surface  mixture. 

In  one  of  these  cities  for  many  years  river  sands  were  in  use 
in  the  surface  mixture  without  the  fine  bank  sand  now  mixed 
with  it.  The  river  sands  would  not  carry  a  sufficient  percentage 
of  asphalt  and  made  a  surface  which  marked  badly  under  traffic, 
perhaps  more  from  their  coarseness  than  from  other  reasons,  but 
which,  in  comparison  with  the  coarse  Washington  mixtures  of 


THE    MINERAL    AGGREGATE. 


41 


Potomac  River  sand,  which  do  not  mark  in  the  same  way,  shows 
a  decided  difference  in  character,  not  due  to  the  size  of  the  particles 
of  which  it  is  composed. 

Two  typical  surface  mixtures  from  the  two  cities  will  illustrate 
the  difference  due  to  the  sand.  A  street  in  the  western  city  marks 
up  more  than  most  of  the  pavements  in  that  town,  that  is  to  say, 
badly.  The  average  mixture  laid  in  Washington  in  1894  with 
a  straight  Potomac  River  sand  scarcely  marked  at  all.  The  com- 
position of  these  two  mixtures  is  as  follows: 


Kansas 
City,  1893. 

Washington, 
1894. 

Bitumen. 
Passing  2 

"       1 
tt 

tt 
tt 
tt 
tt 
tt 

9.9% 
9.0 
6.3 
5.4 
36.3 
10.8 
8.2 
6.5 
7.6 

100.0 

10.9% 
9.9 
1.5 
3.7 
16.1 
28.9 
20.7 
5.9 
2.4 

100.0 

00-mesh  sie 
00- 
80- 
50- 
40- 
30- 
20-    "        ' 
10-    "        ' 

< 

i 

It  would  be  natural  to  expect  that  the  Washington  mixture 
with  the  higher  percentage  of  bitumen  and  coarser  sand  would 
be  the  softer  and  mark  more  than  the  western  mixture,  but  that 
is  not  the  case.  With  a  grading  not  far  different  and  apparently 
less  favorable,  the  Potomac  sand  will  carry  1  per  cent  more  bitu- 
men than  that  in  use  in  the  West  and  still  not  mark  in  hot  weather. 
The  possible  difference  in  sands  from  different  rivers  is  well  illus- 
trated in  this  case. 

As  striking  differences  are  to  be  seen  between  the  mixtures 
made  with  river  sand  in  two  western  cities,  which  may  be  denoted 
No.  1  and  No.  2.  It  is  not  difficult  to  get  sands  in  either  city  which 
can  be  properly  graded  to  our  present  accepted  standard  and 
which,  it  would  be  supposed,  from  all  appearances  would  make 
equally  excellent  asphalt  surface  mixtures.  On  making  the  mix- 
tures, however,  it  is  found  that  the  river  sand  at  city  No.  1  would 
not  hold  the  usual  amount  of  asphalt  cement  and  that  the  varia- 
tions in  amount  from  one  box  of  mixture  to  another  was  so  great 
as  to  make  any  uniformity  in  working  impossible. 


42 


THE    MODERN    ASPHALT    PAVEMENT. 


River  Sand  at  City  No.  i. — In  1896  an  attempt  was  made  to 
devise  a  satisfactory  mixture  for  work  in  this  city.  A  coarse 
sand  was  obtained  from  one  river  and  a  fine  sand  from  another. 
They  had  the  following  mesh  composition: 


Passing  200-mesh  sieve  

0% 

19% 

"        100-    "               

5 

42 

"         80-    "              

11 

19 

"         50-    "              .... 

42 

18 

"         40-    " 

20 

2 

"         30-    "              

16 

0 

"         20-    "         "    

4 

0 

"         10-    "         "    

2 

0 

100 

100 

These  sands  were  combined  in  such  proportions  as  to  make  a 
suitable  grading  and  asphalt  cement  added  until  the  paper  test 1 
showed  a  suitable  amount.  The  mixed  sand  would  hold  at 
the  most  but  142  pounds  of  asphalt  cement  to  the  9-foot  box  of 
material,  and  would  frequently  carry  only  126  pounds,  and  yet 
the  mixture  was  very  sloppy,  where  a  New  York  mixed  sand, 
weighing  about  the  same  per  cubic  foot,  would  carry  over  160 
pounds  and  stand  up  firmly. 

The  grading  of  the  western  sand  and  that  from  New  York, 
for  comparison,  was  as  follows: 


City  No.  1. 

New  York. 

Passing  200-mesh  sieve  

4% 

6% 

"        100-    "         "    

12 

12 

"         80-    '"         "    ... 

14 

12 

"         50-    "         "    

37 

26 

"         40-    "         "    

13 

24 

"         30-    "         "    

10 

8 

a         20-    "         " 

5 

7 

"         10-    "         lt    

5 

5 

Weight  per  9-foot  box,  Ibs  

100 

846 

100 
875 

"    cubic  foot,  Ibs  

94 

97 

A  C  per  box,  Ibs 

126-142 

163 

Per  cent  Trinidad  A.  C.  in  mixture  

13.0-14.0 

15  7 

Pages  352-356. 


THE    MINERAL   AGGREGATE. 


43 


It  is  impossible  at  present  to  explain  the  difference  between 
the  two  sands,  but  it  must  be  one  of  shape  and  surface  of  the  grains 
rather  than  of  volume  per  cent  of  voids,  there  being  no  great 
difference  between  them  in  this  respect. 

The  use  of  these  sands  was  abandoned  for  the  reasons  which 
have  been  given,  although  the  work  done  with  the  mixture  made 
at  that  time  has  been  fairly  satisfactory.  Such  a  mixture  required 
too  much  watching  owing  to  the  rapid  changes  in  proportions 
which  were  necessary.  The  experience  has  proved,  however,  very 
instructive  and  has  shown  that  many  mushy  mixtures  do  not 
prove  as  bad  under  traffic  as  they  look  when  hot,  but  may  give 
good  service ;  and  that  the  asphalt  cement  with  such  s^nd  may  be 
held  at  a  point  as  shown  by  the  paper  stain,  which  with  sand 
from  other  sources  would  be  dangerous. 

Later  the  sands  in  use  in  this  city  were  both  taken  from  the 
same  river,  one  being  a  coarse  sand  and  the  other  finer.  They 
have  been  carefully  selected  by  the  yard  foreman,  who.  has  gone 
out  with  his  sieves  on  the  dredge  and  taken  only  sand  of  a  certain 
grade. 

Typical  specimens  of  these  river  sands  sift  as  follows: 


Coarse. 

Fine. 

1896. 

18 

99. 

1898. 

18 

99. 

Passing  200-mesh  sieve 
."       100-     ' 

$ 

& 

2% 

20% 
24 

17% 
40 

25% 
42 

11         80-             " 

26 

21 

22 

33 

30 

21 

50- 

42 

28 

28 

17 

10 

10 

40- 

11 

20 

19 

3 

1 

1 

"         30-             " 

6 

10 

10 

1 

1 

1 

"         20- 

8 

9 

10 

2 

1 

0 

"         10- 

4 

6 

5 

0 

0 

0 

100 

100 

100 

100 

100 

100 

Retained  on  10-mesh  sieve 

4% 

44  THE    MODERN    ASPHALT    PAVEMENT. 

And  the  mixed  sands  as  coming  from  the  hopper: 


Passing  mesh.  .  . 
1898 

200 
9% 

100 

14% 

80 
30% 

50 

28% 

40 

7% 

30 

4% 

20 

5% 

10 
3% 

-100% 

1899  

6 
10 

10 
9 

25 
25 

36 
9 

9 
16 

11 

3 
9 

11 

=  100 
=  100 

13 
5 
17 

13 

7 
13 

18 
18 
17 

22 

27 
18 

15 
21 
15 

9 
9 
9 

6 
9 

7 

4 
4 
4 

=  100 
=  100 
=  100 

The  sands  in  1898  and  1899  carried  from  154  to  165  pounds 
of  asphalt  cpment  to  the  9-foot  box  and  are  more  satisfactory  than 
those  previously  in  use  on  account  of  their  greater  regularity. 
The  later  mixtures  have  averaged  in  composition  as  follows,  which 
may  be  compared  with  that  made  formerly  with  the  unsatisfactory 
sand: 


Earlier  Sand. 

Later  Sand. 
First  Year. 

Later  Sand. 
Second  Year. 

Biti 
Pas 

« 

jmen     .           

9.9% 
14.3 
9.4 
13.3 
33.0 
10.3 
6.1 
2.6 
1.1 

100.0 

11.3% 
13.2 
9.7 
14.7 
37.2 
5.7 
3.8 
2.7 
1.7 

100.0 

10.4% 
13.0 
10.0 
9.0 
25.0 
15.0 
8.0 
6.0 
4.0 

100.4 

sing  200-me 
100- 
80- 
50- 
40- 
30- 
20- 
10-    ' 

jsh  sieve    

n 

n 

t 

^ 

t 

t 

t            i 

The  second  mixture  of  the  year  1899,  was  the  most  satisfactory 
of  any  made  up  to  that  time,  but  even  here  undesirable  features 
are  to  be  found,  which  will  be  considered  later. 

The  peculiarities  of  these  sands  are,  however,  very  instructive 
if  at  the  same  time  very  trying  in  the  asphalt  business. 

River  Sand  at  City  No.  2. — In  city  No.  2  the  river  sand  presents 
a  most  desirable  grading,  as  shown  by  the  following  sifting  of  some 
in  use  in  July,  1899: 


THE    MINERAL   AGGREGATE 


45 


200-mesh  sieve 
100- 

80- 

50- 

40- 

30- 

20- 

10- 


3% 
26 
12 
39 
14 

2 

3 

1 

100 


2% 
19 
19 
41 
12 

3 

2 

2 

100 


This  sand  is  peculiar,  however,  in  that  in  making  a  mixture 
according  to  our  practice  it  is  found  that  if  the  asphalt  cement 
is  added  in  amount  only  sufficient  to  stain  the  paper  *  to  the 
same  degree  as  with  the  sands  in  other  cities,  the  bitumen  hi  the 
mixture  does  not  exceed  9  per  cent.  With  a  larger  amount  of 
asphalt  cement,  sufficient  to  yield  10  per  cent  of  bitumen  in  the 
mixture,  the  latter  is  very  sloppy. 

This  peculiarity  might  lie  either  in  the  heavier  volume  weight 
of  the  sand  and  the  smaller  voids  or  in  some  characteristic  of  the 
surface  of  the  grain  which  would  prevent  the  usual  amount  of 
asphalt  cement  from  adhering  to  it.  It  has  been  found,  however, 
on  the  use  of  this  same  sand  in  a  neighboring  city  that  a  satis- 
factory surface  containing  as  much  as  10  per  cent  of  bitumen  can 
be  laid  by  making  the  mixture  as  rich  as  is  necessary  for  this  figure, 
and  disregarding  the  usual  indications  of  richness  and  overfill- 
ing of  the  voids.  The  finished  surface  does  not  appear  to  be  exces- 
sively soft  in  summer  and  wears  well.  This  would  point  to  the 
correctness  of  the  idea  that  the  peculiarity  of  this  sand  lies  in  its 
surface  and  perhaps  in  its  shape.  Nothing  peculiar  in  either  of 
these  respects,  as  far  as  can  be  seen  under  the  microscope,  can  be 
discovered,  the  sand  being  a  nearly  pure  quartz,  having  a  ground- 
glass  surface  with  rounded  angles.  Fig.  2,  No.  3. 

In  considering  the  subject  of  mixtures  these  peculiar  sands 
will  be  referred  to  again.2 

1  This  paper  test  will  be  described  later,  pages  352-356,  514.     It  indicates 
the  amount  of  asphalt  the  sand  will  carry. 

2  Page  351. 


46  THE   MODERN    ASPHALT    PAVEMENT. 

The  river  sands  of  the  United  States  in  the  Mississippi  Valley 
seem,  therefore,  to  be  possessed  of  peculiar  properties  which  we 
are  unable  as  yet  to  account  for,  and  it  is  necessary  to  handle 
them  in  the  paving  industry  in  a  different  way  from  other  sands, 
or  else  to  reject  them. 

Bank  or  Pit  Sands. — Bank  or  pit  sands  are  deposits  of  sand 
which  have  been  laid  down  in  their  present  position  by  various 
agencies  in  past  geological  times,  as  distinguished  from  the  river 
and  beach  sands,  which  have  been  described  and  which  are  the 
results  of  the  recent  assorting  of  detritus  by  water  action,  or  by 
the  reasserting  of  bank  sands  under  changed  conditions,  which 
is  quite  possible,  as  on  the  north  shore  of  Long  Island,  where  the 
glacial  bank  sands  are  often  reasserted  by  water  action  into  modern 
beach  sands. 

Bank  sands  are  of  the  most  varied  derivation — river,  beach, 
glacial,  seolian,  etc. — including  all  possible  sources  of  origin.  On 
the  Hudson  are  found  banks  of  river  sand,  as  at  Croton ;  on  Long 
Island  banks  of  glacial  sand,  as  at  Cow  Bay,  and  in  Sioux  City, 
Iowa,  banks  of  seolian  sand  in  the  loess. 

Bank  sands  grade  in  size  from  fine  gravel  or  coarse  concrete 
sand  to  the  impalpably  fine  ones  which  are  found  in  those  wind- 
blown deposits  of  a  large  portion  of  the  West,  called  loess,  and 
which  are  often  almost  entirely  a  sharp  sand  composed  of  quartz 
particles  fine  enough  to  pass  a  200-mesh  sieve. 

To  the  paving  industry  the  bank  sands  offer  sources  of  sup- 
plies which  are  more  varied  in  the  size  of  the  particles  of  which 
the  sand  is  made  up  than  the  river  and  beach  sands  of  recent 
origin,  and  are  oftener  to  be  obtained  of  that  degree  of  fineness 
which  has  been  found  to  be  such  an  essential  feature  in  our  modern 
mixtures,  that  is  to  say,  of  80-  and  100-mesh  size.  The  varied 
grading  of  different  bank  sands,  not  including  the  coarser  con- 
crete supplies  which  are  not  used  in  the  asphalt  industry  for  sur- 
face mixture,  is  illustrated  by  the  following  characteristic  speci- 
mens (see  table,  p.  47). 

These  bank  sands,  it  will  be  seen,  admit  of  combinations  of  two 
or  more  in  such  a  way  as  to  attain  any  required  grading.  Fortu- 
nately no  bank  sands  are  met  with  which  present  any  of  the  pecu- 


THE    MINERAL   AGGREGATE. 


47 


liarities  of  the  river  sands  of  the  Mississippi  River  Valley, 
all  carry  asphalt  well  and  make  good  mixtures. 


They 


New  York  Supply,  1899. 

Boston  Supply. 

Passing  Sieve 
of  Meshes. 

Cow  Bay. 

Corbin's 
Bank, 
Steinway. 

Delagoa 
Bay 
Ballast. 

Braintree, 
Mass. 

Canton, 
Mass. 

200 

4% 

2% 

6% 

1% 

12% 

7% 

100 

5 

10 

60 

25 

13 

80 

9 

7 

12 

36 

15 

14 

50 

28 

24 

28 

2 

29 

33 

40 

22 

16 

15 

1 

9 

19 

30 

15 

18 

13 

0 

6 

6 

20 

9 

13 

10 

0 

2 

6 

10 

6 

15 

6 

0 

2 

2 

100 

100 

100 

100 

100 

100 

Buffalo 
Supply, 
Attica,  N.  Y. 

Elmira 
Supply. 

Utica  Supply. 

Lafayette 
Supply. 

Toronto, 
Ontario, 
Supply. 

200 

32% 

6% 

8% 

3% 

29% 

100 

29 

7 

31 

5 

36 

80 

17 

38 

25 

4 

14 

50 

19 

48 

20 

36 

13 

40 

1 

1 

12 

37 

2 

30 

1 

0 

2 

10 

6 

20 

1 

0 

1 

3 

0 

10 

0 

0 

1 

2 

0 

100 

100 

100 

100 

100 

Kent,  England,  Glacial. 

Louisville  Bank. 

Sioux  City. 

White. 

Yellow. 

200 

o% 

tr. 

48% 

99.5% 

100 

11 

4% 

20 

.5 

80 

74 

28 

11 

50 

14 

62 

18 

40 

1 

6 

1 

30 

tr. 

tr. 

2 

20 

0 

0 

0 

10 

0 

0 

0 

100 

100 

100 

100.0 

48  f  HE    MODERN    ASPHALT    PAVEMENT. 


bank  satids  are  unsuitable  for  use  in  the  surface  mixture, 
however,  owing  to  the  presence  of  too  much  clay  or  loam,  or  to  a 
surface  on  the  grain  which  is  more  or  less  covered  with  a  ferru- 
ginous cement,  existing  in  the  original  rock  from  which  the  sand 
is  derived,  or  with  argillaceous  matter,  to  neither  of  which  surfaces 
does  asphalt  adhere  satisfactorily.  The  former  peculiarity  is  of 
the  commonest  occurrence,  but  probably  only  becomes  serious 
when  the  amount  of  clay  or  loam  is  too  large  to  be  taken  care  of 
as  dust,  or  is  in  such  a  form  as  to  ball  up  in  the  sand-heating 
drums,  or  not  to  mix  with  the  asphalt  cement  properly.  A  loamy 
tempering  sand  has  been  in  use  successfully  in  an  Ohio  River 
city  for  several  years.  The  latter  difficulty  is  typical  of  the  red 
sands  of  New  Jersey,  which  have  a  coating  of  iron  oxide  firmly 
adherent  to  their  surfaces,  and  the  sands  found  associated  with 
the  London  gravels  which  are  similarly  but  not  so  distinctively 
coated.  From  the  latter  sand  a  coating  of  asphalt  cement  would 
wash  off  in  a  few  weeks  when  exposed  to  the  weather,  destroying 
the  surface  mixture  made  with  it.  The  red  sands  of  New  Jersey 
may  possibly  be  used  without  danger;  that  from  Rutherford  has 
been  as  a  tempering  sand,  but  they  do  not  look  attractive  and 
are  suspicious. 

There  are  no  other  noticeable  peculiarities  of  bank  sands  to 
be  mentioned  which,  as  far  as  is  known,  render  them  unsuited 
for  surface  mixtures,  except  the  presence  of  too  much  200-mesh 
material  which  consists  of  sand  grains  of  that  size  and  not  dust. 
Sand  of  this  size  is,  as  a  rule,  disadvantageous  in  a  mixture  and 
makes  it  mushy  and  liable  to  push  or  shove  under  traffic.  The 
peculiarities  of  mixtures  containing  much  200-mesh  sand  will  be 
discussed  later. 

Quicksands.  —  Any  of  the  preceding  sands  is  often  called  quick- 
sand if  it  is  very  fine.  Quicksands  are  really  of  that  peculiar 
nature  only  when  they  consist  of  particles  largely  finer  than  will 
pass  a  sieve  of  200  meshes  to  the  inch  and  consequently  having 
a  small  hydraulic  value.  When  such  sands  have  their  voids  filled 
or  more  than  filled  with  water  they  are  unstable  and  mobile.  There 
is  no  reason  why  a  coarse  sand  should  not  at  the  same  time  be  a 
quicksand  if  it  is  supported  and  its  voids  more  than  filled  by  a 


THE    MINERAL   AGGREGATE. 


49 


force  of  water  of  sufficient  head.  It  has  often  been  stated  that 
quicksands  consist  of  uniform  sized  and  round  particles,  but  recent 
examination  of  some  material  of  this  description1  has  shown  that 
they  generally  consist  of  sharp  grains  and  are  often  well  graded. 
Several  quicksands  have  been  examined  by  the  writer  with  the  fol- 
lowing results,  which  are  characteristic  of  such  material : 

QUICKSANDS— BOSTON,  1897;  WORCESTER,  1900. 

Test  No.  11541.  Boston— Neponset  Valley  Sewer.     Nat.  Contr  Co. 
it       it    11542         "  "  "  "  "         "        " 

"  "  11544         "                lt  "  ll            "         "        " 

"  "  30723.  Worcester— Green  Street.  H.  P.  Eddy. 

"  "  30724           ' '                 "  "  «    «      « 

it  «  QQ725           "                 "  "  it    u      « 

Finest-ground  limestone,  all  passing  200  mesh. 

Xos.  11541,  11542,  and  30725  are  clean  sands,  grains  all  sharp.  Nos. 
11544,  30723,  and  30724  contain  a  small  amount  of  clay,  less  than  1  per  cent, 
not  subsiding  entirely  in  one  week. 


Test  Nc 

Voids  in 
pacte( 
Weight 
foot  o 
pounc 

Sieve. 

200 
100 
80 
50 
40 
30 
20 
10 

s  

hot  com- 
i  sand.  .  . 
per  cubic 
same  in 

s  .  . 

11541 
29.3% 
117.2 

11542 

11544 
40.2% 
99.1 

65.5% 
13.7 
17.8 
2.0 
1.0 

30723 
36.7% 
103.8 

47.2% 
19.6 
11.2 
13.0 
4.0 
3.0 
1.0 
1.0 

30724 
34.7% 
106.1 

11.6% 
11.4 
9.0 
39.0 
12.0 
10.0 
3.0 
3.0 
1.0 

30725 

Finest- 
ground 
Lime- 
stone. 

39.3% 
100.4 

63.5% 
17.7 
18.8 

Diameter, 
Milli- 
meters. 

.035 
.065 
.09 
.17 
.23 
.31 
.50 
.67 
1.00 
2.00 

Greater 
than  2. 

19.2% 
7.9 
18.9 
34.0 
11.0 
7.0 
1.0 
1.0 

H.2% 
14.2 
19.6 
22.0 
8.0 
16.0 
4.0 
2.0 
2.0 

79.7% 
9.5 
9.8 
1.0 

1.0 

100.0 

100.0 

100.0 

100.0 
2.0% 

1CO.O 

100.0 

100.0 

1  Landreth,  Wm.  B.,  The  Improvement  of  a  Portion  of  the  Jordan  Level 
of  the  Erie  Canal.     Trans.  Am.  Soc.  C.  E.,  1900,  43,  596. 


50  THE    MODERN    ASPHALT    PAVEMENT. 

It  is  apparent  that  some  quicksands  are  quite  widely  graded, 
others  consist  to  a  very  large  extent  of  uniform  particles  smaller 
than  .035  millimeter  in  diameter  (.0014  inch)  and  even  finer  than 
the  finest  dust  in  Portland  cement.  That  they  are  all  composed 
of  sharp  grains,  contain  traces  only  of  clay  or  none,  have  an  ex- 
traordinary fineness,  in  one  case  greater  even  than  that  of  the 
best  ground  limestone,  are  their  astonishing  characteristics. 

The  angularity  of  these  small  particles  is  explained  by  their 
small  hydraulic .  value  and  consequent  freedom  from  attrition, 
as  shown  by  some  experiments  of  Daubree,  quoted  by  Geikie, 
Text-book  of  Geology,  third  edition,  page  385.  He  says: 

"In  the  series  of  experiments  already  referred  to,  Prof.  Daubree 
made  fragments  of  granite  and  quartz  to  slide  over  each  other 
in  a  hollow  cylinder  partially  filled  with  water  and  rotating  on 
its  axis  with  a  mean  velocitiy  of  .80  to  1  metre  in  a  second.  He 
found  that  after  the  first  25  kilometers  (about  15J  English  miles) 
the  angular  .fragments  of  granite  had  lost  T4¥  of  their  weight, 
while  in  the  same  distance  fragments  already  well  rounded  had 
not  lost  more  than  -j-J-^  to  J}Q.  The  fragments  rounded  by  this 
journey  of  25  kilometers  in  a  cylinder  could  not  be  distinguished 
either  in  form  or  general  aspect  from  the  natural  detritus  of  a  river- 
bed. A  second  product  of  these  experiments  was  an  extremely 
fine  impalpable  mud,  which  remained  suspended  in  the  water 
several  days  after  cessation  of  the  movement.  During  the  pro- 
duction of  this  fine  sediment  the  water,  even  though  cold,  was 
found  in  a  day  or  two  to  have  acted  chemically  upon  the  granite 
fragments.  After  a  journey  of  160  kilometers,  3  kilograms 
(about  6J  pounds  avoirdupois)  yielded  3.3  grams  (about  50 
grains)  of  soluble  salts,  consisting  chiefly  of  silicate  of  potash. 
A  third  product  was  an  extremely  fine  angular  sand  consisting 
almost  wholly  of  quartz,  with  scarcely  any  feldspar,  nearly  the 
whole  of  the  latter  mineral  having  passed  into  the  state  of  clay. 
The  sand  grains  as  they  are  continually  pushed  onward  over  each 
other  upon  the  bottom  of  a  river  become  rounded  as  the  large 
pebbles  do.  But  a  limit  is  placed  to  this  attrition  by  the  size 
and  specific  gravity  of  the  grains.  As  a  rule  the  smaller  particles 
suffer  proportionately  less  loss  than  the  larger,  since  the  friction 


THE    MINERAL   AGGREGATE.  51 

on  the  bottom  varies  directly  as  the  weight  and  therefore  as  the 
cube  of  the  diameter,  while  the  surface  exposed  to  attrition  varies 
as  the  square  of  the  diameter.  Mr.  Sorby,  in  calling  attention  to 
this  relation,  remarks  that  a  grain  y1^  of  an  inch  in  diameter 
would  be  worn  ten  times  as  much  as  one  T^o  of  an  inch  in  diameter, 
and  a  pebble  1  inch  in  diameter  would  be  worn  relatively  more  by 
being  drifted  a  few  hundred  yards  than  a  sand  grain  y^  of  an 
inch  in  diameter  would  be  by  being  drifted  for  a  hundred  miles. 
So  long  as  the  particles  are  borne  along  in  suspension,  they  will 
not  abrade  each  other,  but  remain  angular.  Prof.  Daubree  found 
that  the  milky  tint  of  the  Rhine  at  Strasburg  in  the  months  of 
July  and  August  was  due,  not  to  mud,  but  to  a  fine  angular  sand 
(with  grains  about  -£$  millimeter  in  diameter)  which  constitutes 
TTJ«irinr  of  the  total  weight  of  the  water.  Yet  this  sand  had 
travelled  in  a  rapidly  flowing  tumultuous  river  from  the  Swiss 
mountains,  and  had  been  tossed  over  waterfalls  and  rapids  in  its 
journey.  He  ascertained  also  that  sand  grains  with  a  mean  diam- 
eter of  TV  mm.  will  float  in  feebly  agitated  water,  so  that  all 
sand  of  finer  grains  must  remain  angular.  The  same  observer  has 
noticed  that  sand  composed  of  grains  with  a  mean  diameter  of 
£  mm.  and  carried  along  by  water  moving  at  a  rate  of  1  metre  per 
second  is  rounded  and  loses  about  y  o^W  °f  its  weight  in  every 
kilometer  travelled." 

These  remarks  explain  some  of  the  characteristics  of  the  quick- 
sands which  have  been  described. 

So-called  quicksands  consisting  largely  of  particles  of  100- 
and  80-mesh  size  form  one  of  the  most  valuable  sand  supplies  which 
can  be  used  in  the  paving  industry.  They  are  known  as  temper- 
ing sands,  and  when  mixed  with  the  ordinary  sand  produce  a 
grading  which  is  more  satisfactory  than  that  of  any  sand  deficient 
in  such  fine  particles. 

Glacial  Sand. — Such  sands  are  found  on  the  north  shore  of 
Long  Island  and  are  largely  used  in  the  paving  industry  in  the 
city  of  New  York.  Fig.  2,  No.  4. 

In  those  parts  of  the  country  which  were  covered  with  the 
ice  sheet  during  the  Glacial  Period  a  large  part  of  the  beach,  lake, 
and  river  sands  may  consist  of  glacial  material  reasserted  by 


THE    MODERN    ASPHALT    PAVEMENT. 


more  recent  water  action,  but  this  is,  of  course,  not  true  of  sands 
from  regions  south  of  the  terminal  moraine,  nor  is  it  probably 
the  case  with  the  sands  found  in  our  western  rivers,  which  are 
of  very  recent  origin.  This  may  account  for  the  fact  that  the 
sands  from  the  Mississippi  and  Missouri  Rivers  and  their  tribu- 
taries are  so  different  from  many  other  river  sands. 

Sands  Derived  from  Sandstones. — Supplies  of  sand  are  to  be 
found  at  times  which  are  obtained  by  grinding  and  breaking  down 
loose  sandstones  of  little  coherence.  These  sands  are  largely  used 
in  glass-making  and  are  usually  very  fine  quartz.  They  have 
been  offered  in  several  cities  for  paving  purposes.  Two  samples 
sifted  as  follows: 


Passing  200-mesh  sieve 

5% 

5% 

'  '        100-              '  ' 

7 

15 

"         80-             " 

13 

22 

"         50-             "    

45 

40 

"         40-             "    

25 

15 

"         30-             "    

2 

1 

"         20-             "    

1 

1 

"         10-             " 

2 

1 

100 

100 

They  have  never  been  utilized  in  the  paving  industry. 

Artificial  Sands. — The  finer  material  produced  in  crushing 
rock  for  the  purpose  of  obtaining  broken  stone  for  concrete  when 
screened  to  a  proper  size  is  a  sand.  It  differs  essentially  from 
the  natural  sands  in  that  it  has  not  been  subjected  to  weathering 
or  attrition  and  consequently  is  sharp  and  has  a  rough  surface. 
Fig.  2,  No.  5.  It  is  generally  well  graded  through  different 
sizes  and  has  low  voids.  Specimens  of  such  a  sand  are  represented 
by  the  screenings  from  the  crushing  of  granite,  gneiss,  limestone, 
and  trap  in  various  parts  of  the  East,  which  sift  as  follows: 

Test  No.  68417.  Crushed  gneiss  screenings  from  Jerome  Park  Reservoir, 

New  York. 

"      "    66563.  Trap-rock  screenings,  Nyack,  N.  Y. 
"      "    62082.  Limestone  screenings,  Muskegon,  Mich. 
"      "    64840.  "  "  Owosso,  Mich. 

"      "    69721.  "  "  Harrisburg,  Pa. 

"  "          Washington,  D.  C. 


THE    MINERAL    AGGREGATE. 


63 


Tes 
Pas 

< 

t 

Ret 

t  number  

68417 

6.5% 
7.5 
5.0 
12.5 
12.5 
8.0 
10.0 
8.0 
17.0 
3.5 
9.5 
0.0 

66563 

10.5% 
7.5 
2.5 
7.0 
4.0 
5.0 
5.5 
15.5 
34.0 
8.5 
0.0 

J  o.o 

62082 

17% 
3 

64840 

7% 
5 
4 
8 
5 
5 
6 
18 
42 
0 
0 
0 

69721 

28% 
12 
7 
13 
9 
9 
11 
11 
0 
0 
0 
0 

21% 
14 
8 
11 
8 
6 
8 
19 
5l 

100 

sing  200-rm 
100- 
80- 
50- 
40- 
30- 
20- 
10- 
1-incl 

1         *-  " 
1-  " 
ained  on  1- 

;sh  sie 

i 

inch  s 

ve 
ie\ 

e 

52 

28  l 



100.0 

100.0 

100 

100 

100 

1  Retained  on  10  mesh. 

These  screenings  are  of  excellent  character  for  use  in  hydraulic 
concrete  and  have  also  been  successfully  made  part  of  the  mineral 
aggregate  of  surface  mixtures,  as  the  finer  material  which  they 
contain  is  very  desirable  in  localities  where  the  particles  of  the 
same  size  are  not  found  in  the  native  sand. 

The  screenings  from  the  softer  limestones  of  the  middle  and 
far  West  are  not  so  desirable  as  a  substitute  for  native  sand,  and 
no  attempt  has  been  made  to  use  them  in  an  asphalt-surface  mix- 
ture as  sand.  When  ground  they  form  a  most  desirable  filler,  as 
they  readily  become  impregnated  with  asphalt. 

Purchase  of  Sands. — Iu  this  connection  it  may  be  well  to  state 
that  no  sand  is  desirable  for  use  in  an  asphalt-surface  mixture 
which  would  be  considered  suitable  for  use  in  lime  or  cement  mortar. 
It  is  therefore  often  difficult  to  explain  to  sand-dealers  the  kind 
of  sand  needed  in  the  asphalt  industry  and  more  often  difficult 
to  find  it,  as  there  is  no  demand  for  such  sand  from  others  and 
consequently  little  inducement  to  open  up  or  develop  pits  or 
supplies  of  the  proper  kind.  It  is  well  usually  to  say,  in  asking  a 
sand-dealer  for  sands  for  surface  mixtures,  that  one  wishes  a  sand 
that  is  too  "soft"  for  any  other  use,  and  that  one  which  is  suitable 
for  mortar  would  be  of  no  value  for  pavements. 

Composition. — The  composition  of  a  sand,  as  long  as  the  grains 
are  hard,  cannot  seriously  affect  its  availability  for  use  in  an  asphalt- 


54  THE    MODERN    ASPHALT    PAVEMENT. 

surface  mixture  or  be  a  cause  of  defects  in  it.  Soft-grained  sand 
should  be  rejected  when  this  is  possible.  The  grains  of  a  very  large 
majority  of  all  the  sands  in  use  in  the  asphalt  industry,  in  fact 
of  almost  all  natural  sands,  are  composed  of  quartz,  the  silicates, 
feldspar,  etc.,  being  decomposed  and  removed  from  the  detritus 
of  the  original  rock  by  weathering  or  water  action.  The  character 
of  the  quartz  may  vary  largely,  however.  It  may  be  a  clear,  trans- 
parent, hard  quartz,  a  softer  cloudy-white  quartz,  or  an  even  softer 
ferruginous  one.  The  two  latter  suffer  more  from  attrition,  have 
round  forms  and  dead  surfaces.  Rarely  sands  are  found  which 
consist  of  a  large  proportion  of  silicates  or  of  shales,  although  a 
small  amount  of  magnetite  and  the  harder  pyroxenes  are  to  be 
detected  in  most  sands.  Potomac  River  sand  often  carries  3  per 
cent  of  magnetite,  and  that  from  Siboney  beach,  which  has  been 
used  in  Santiago,  Cuba,  must  consist  fully  half  of  hard  silicates 
such  as  hornblende  and  similar  minerals,  which  are,  however,  not 
unsuitable  for  paving  purposes.  A  sand  formed  by  weathering 
of  a  granite  rich  in  feldspar  on  Cape  Neddick  in  Maine  is  largely 
made  up  of  coarse  particles  of  feldspar,  but  it  is  not  of  any  prac- 
tical importance. 

The  sand  found  in  the  Mohawk  and  Hudson  River  Valleys 
from  Poughkeepsie  to  Geneva  consists  largely  of  small  oval  and 
flat  particles  of  shale,  although  some  quartz  is  present.  These 
sands  are,  of  course,  comparatively  soft,  but  good  work  for  light 
traffic  has  been  done  with  them. 

Calcareous  sands  are  rather  unusual,  except  those  derived 
from  shells  and  the  detritus  of  coral.  Limestones  weather  out 
or  dissolve  too  rapidly  in  water  to  permit  of  the  formation  of 
sand,  although  they  are  found  to  a  certain  extent  in  admixture 
with  quartz  sands  at  many  points. 

Coral  and  shell  sands  are  common  in  southern  latitudes,  as 
in  Cuba  and  Bermuda,  for  instance.  They  are  the  softest  sands 
that  are  met,  usually  crumbling  under  moderate  pressure.  Few 
particles  finer  than  80-mesh  size  are  found  in  the  coral  sands, 
as  these  are  readily  washed  away  and  dissolved.  The  shell  sands 
of  Cuba  are  firmer  than  the  coral  sands. 

Mixed  sands  composed  of  quartz  and  silicates,   and  quartz 


THE    MINERAL   AGGREGATE. 


65 


and  carbonates,  occur.  Such  include  the  more  evenly  propor- 
tioned Siboney  beach  sand  and  the  shale  sand  of  Northern  New 
York.  The  lake  sands  often  contain  considerable  carbonates 
in  the  form  of  shells,  and  a  small  amount  is  found  in  almost  all. 
Determinations  of  lime  in  several  supplies,  made  in  1896,  gave 
the  following  results: 


Source  of  Sand. 

Per  Cent  CaO. 

Buffalo  —  lake             

9  3% 

New  York  —  bank  

2  2 

St  Louis  —  river  

8 

Kansas  City  —  river 

2 

Boston  —  bank 

2 

Their  presence  has  no  injurious  influence  on  the  sand  as  far 
as  its  use  in  asphalt  surface  mixture  is  concerned.  Asphalt  cements 
probably  adhere  better  to  limestone  than  to  silica  or  silicates,  and 
in  this  way  it  may  be  desirable. 

It  is  sometimes  of  interest  to  determine  how  much  or  what 
percentage  of  a  sand  is  in  a  condition  soluble  in  strong  acid,  such 
as  hydrochloric.  The  amount  found  in  the  sands  mentioned 
above,  which  were  examined  for  lime,  was  as  follows: 


Source  of  Sand. 

Per  Cent 
Soluble. 

Per  Cent  Iron 
Oxide  and 
Aluminum. 

St  Louis  —  river                   

2.2% 

9% 

Kansas  City  —  river  

2.4 

1.4 

New  York  —  bank  

3.4 

2.3 

Boston  —  bank        

3.6 

2.4 

Buffalo  —  lake  

12.9 

1.5 

In  the  ordinary  run  of  sand  this  is  small  and  of  no  importance. 
In  some  of  the  sands,  like  the  red  sands  of  New  Jersey,  it  is  indic- 
ative of  a  weakness  in  the  material. 

Sands  may  often  carry  admixtures  of  substances  which  cannot 
be  considered  as  part  of  the  original  material  from  which  they 
have  been  derived  but  which  are  adventitious  in  some  way  or 


56  THE    MODERN    ASPHALT    PAVEMENT. 

other.  Clay  and  loam  are  the  commonest  substances  and  their 
presence  is  accounted  for  in  two  ways.  Either  they  are  inti- 
mately mixed  with  the  sands  in  the  deposits,  as  in  the  fine  bank 
sand  mentioned  as  being  used  for  tempering  purposes,  or  they 
exist  in  strata  covering  or  adjacent  to  the  sand  and  are  unavoid- 
ably mixed  with  it  in  collecting  the  latter.  If  not  adherent  to 
the  grain  a  small  amount  will  act  merely  like  the  dust  added  to 
the  sand  before  the  asphalt  cement,  but  if  the  clay  or  loam  balls 
in  the  drums  and  is  not  screened  out  it  may  prove  injurious. 
A  clean  sand  is  in  any  case  probably  more  desirable,  although 
satisfactory  results  have  been  obtained  with  many  loamy  ones. 
Organic  matter  in  the  shape  of  vegetable  debris  is  sometimes 
found  in  sand.  It  is  usually  removed  in  screening  the  hot  sand 
as  it  comes  from  the  drums.  If  this  is  not  possible  and  the  amount 
remaining  is  excessive  the  sand  should  be  rejected. 

Shape  of  Sand  Grains. — The  shape  of  the  grains  of  which  sands 
are  composed  is  quite  varied. 

Irregular  Grains. — Fresh  detritus  from  the  original  rock 
is  generally  irregular  in  shape  and  with  sharp  angles  unless  it  is 
derived  from  a  rock  composed  of  grains  which  have  already  existed 
as  sand.  Sands  formed  of  irregular  grains  are  not  common,  but 
they  are  often  found  with  the  grain  quite  irregular  in  shape  but 
the  angles  somewhat  rounded  by  water  or  glacial  action.  The 
sands  from  the  north  shore  of  Long  Island  are  of  this  class.  Fig.  2, 
No.  4,  shows  the  peculiarity  of  the  grain.  They  are  of  very  irregu- 
lar shape  with  re-entrant  angles,  but  are  slightly  rounded  with 
loss  of  the  sharpness  of  the  original  fragment. 

Crystalline  Grains. — Sands  containing  crystals  are  mentioned 
by  Sorby.  They  have  been  met  with  by  the  author  but  once  in 
the  United  States.  In  a  sand  supply  used  in  Atlanta,  Ga.,  some 
years  ago,  there  could  be  detected  with  a  glass  quite  a  large  pro- 
portion of  well-shaped  quartz  crystals  some  of  which  were  twins. 
Fig.  2,  No.  6,  shows  the  irregular  weathered  crystals  forming  this 
sand. 

Such  sands  are  undesirable  for  an  asphalt  surface  mixture  for 
reasons  too  obvious  to  require  mention. 

Oval  Grains  are  worn  much  more  smooth  by  continued  water, 


THE    MINERAL   AGGREGATE.  57 

tidal  or  glacial  action,  the  original  angles  being  mostly  or  entirely 
lost.  Tidal  action  has  a  peculiar  tendency  to  produce  grains  with 
one  diameter  longer  than  the  other,  as  particles  with  this  peculiarity 
arrange  themselves  with  their  longer  diameter  in  the  direction  of 
the  force  of  the  waves  and  are  then  worn  still  more  into  this  shape. 
Seabeach  sands  are  supposed  on  this  account  to  be  far  from  sharp, 
but  that  on  the  Florida  beaches  is  markedly  so.  Fig.  2,  No.  1. 

Round  Grains.— Round-grained  sands  are  not  uncommon.  They 
are  oftener  found  in  river,  glacial,  and  aeolian  sands,  which  are 
worn  by  being  rolled  over  and  over  and  polished  against  each 
other  like  the  well-known  spheres  of  quartz  prepared  by  the 
Japanese.  Fig.  2,  No.  7.  It  is  probable  that  a  very  large  per- 
centage of  sand  is  composed  of  the  somewhat  irregular,  rounded 
grains. 

The  shape  of  the  grains  of  a  sand  has  a  marked  influence,  when 
combined  with  their  size  and  grading,  upon  the  character  of  the 
asphalt  surface  mixture  made  with  them,  the  closeness  with  which 
they  can  be  packed  together  depending  to  a  very  considerable 
degree  on  their  shape.  Round  sands  and  oval  sands  can  be  com- 
pressed much  more  readily  than  sharp  ones,  owing  to  the  smaller 
friction  between  the  smooth  surfaces,  although  they  may  not 
on  this  account  be  found  to  pack  as  closely  eventually.  Whether 
the  shape  of  the  grains  in  the  sands  in  use  hi  paving  mixtures  has 
any  effect  sufficient  to  account  for  the  cracking  of  some  surfaces 
more  than  others  is  a  question  for  investigation.  It  may  so 
influence  the  character  of  the  voids  in  a  mineral  aggregate  as  to 
do  so.  This  will  be  considered  later.  Mixtures  made  with  round- 
grained  sands  are  of  course  less  stable  and  mark  more  easily  in 
summer  than  those  made  with  sharp  sand,  since  round  particles 
move  much  more  readily  over  one  another  than  sharp  ones ;  but, 
on  the  other  hand,  with  plenty  of  filler  this  tendency  can  be  neu- 
tralized, while  the  round-grained  sands  can  be  packed  much  more 
readily  and  closely  and  with  smaller  voids  and  the  resulting  sur- 
face can,  in  this  way,  be  made  denser. 

Surface  of  Sand.— The  character  of  the  surfaces  of  sand  grains 
is  very  different,  much  more  so  than  would  appear  from  mere 
ocular  examination.  Under  the  microscope  sand  grains  are  found, 


58  THE    MODERN    ASPHALT    PAVEMENT. 

as  shown  in  our  classifications,  with  the  surfaces  of  the  original 
material  of  which  the  grains  are  composed,  or  with  the  surfaces 
derived  from  fracture  of  this  material.  There  are  surfaces  polished 
by  attrition  and  water  action,  surfaces  like  ground  glass,  Fig.  2, 
No.  7,  originating  in  the  same  way,  surfaces  coated  with  the 
cementing  material  originally  uniting  the  grains  into  a  sandstone, 
surfaces  acted  upon  chemically,  and  the  porous  surfaces  of  lime- 
stone and  coral  grains.  The  different  kinds  of  surfaces  behave 
quite  differently  toward  asphalt  cement.  The  porous  limestone 
surfaces  absorb  it  and  it,  of  course,  adheres  very  firmly.  To 
the  quartz  surfaces  the  bitumen  adheres  in  most  cases  well,  but 
in  others  only  slightly,  being  readily  washed  off  with  water.  Some 
quartz  grains  will  carry  a  heavy  coat  of  asphalt  cement,  others 
but  a  small  and  thin  one,  as  can  be  detected  by  examining  with 
a  glass  mixtures  made  with  different  sands. 

These  peculiarities  can  be  explained  by  the  difference  in  the 
capacity  of  surfaces  of  different  character  for  retaining  or  adsorb- 
ing bitumen,  the  film  adhering  being  thicker  in  one  case  than  in 
another.  They  have  a  very  decided  effect  upon  the  character 
of  different  mixtures  and  may  well  be  the  cause  of  cracking  in 
surfaces  made  with  certain  kinds  of  sand.  As  has  been  already 
remarked,  a  sand  from  the  London  gravels  has  a  surface  such  that 
asphalt  cement  would  not  adhere  to  it  in  the  presence  of  the  damp- 
ness of  a  London  fog,  so  that  it  would  be  found  in  the  gutters 
after  a  rain,  washed  quite  clean  and  free  from  bitumen. 

That  even  water  has  strong  chemical  effect  on  the  surface  of 
sands,  thus  altering  its  character,  can  be  seen  from  Daubree's 
experiments  already  alluded  to.  Geikie  quotes  him  as  follows: 

"Daubree  endeavored  to  illustrate  the  chemical  action  of 
rivers  upon  their  transported  pebbles  by  exposing  angular  frag- 
ments of  feldspar  to  prolonged  friction  in  revolving  cylinders  of 
sandstone  containing  distilled  water.  He  found  that  they  under- 
went considerable  decomposition,  as  shown  by  the  presence  of 
silicate  of  potash,  rendering  the  water  alkaline.  Three  kilograms 
of  feldspar  fragments  made  to  revolve  in  an  iron  cylinder  for  a 
period  of  192  hours,  which  was  equal  to  a  journey  of  460  kilo- 
meters (287  miles),  yielded  2.720  kilograms  of  mud,  while  the 


THE    MINERAL    AGGREGATE.  59 

5  litres  of  water  in  which  they  were  kept  moving  contained  12.60 
grams  of  potash,  or  2.52  grams  per  litre." 

Of  course  quartz  grains  are  not  attacked  like  the  feldspar, 
and  it  is  for  this  reason  that  in  sands  resulting  from  the  decomposi- 
tion of  rocks  containing  feldspar  none  of  the  latter  remains  and 
the  grains  of  which  it  is  composed  are  all  quartz,  hornblende,  etc. 

From  what  has  been  said  in  the  preceding  paragraphs  the  very 
variable  character  of  sand,  apart  from  the  size  of  the  grain,  will 
be  readily  understood.  All  of  these  characteristics  demand  care- 
ful consideration  in  the  selection  of  sands  for  successful  asphalt 
surface  mixtures.  But  more  important  even  than  these  considera- 
tions is  the  size  of  the  grains  whicl^  go  to  make  up  any  sand. 

Size  of  Sand  Grains. — The  size  of  the  sand  grains  in  an  asphalt 
pavement,  that  is  to  say  their  average  diameter,  is  of  the  greatest 
importance,  as  will  be  found  in  studying  the  subject  of  surface 
mixtures.  Sands  occur  hi  nature  in  which  are  found  every  size 
grain  from  the  impalpably  fine  quartz  of  silt  to  fine  gravel.  In  a 
standard  sheet  asphalt  surface  it  has  been  found  generally  prefer- 
able to  have  no  sand  grains  larger  than  2  millimeters  in  diameter, 
passing  a  10-mesh  sieve  made  of  wire  .027"  in  diameter,  or  smaller 
than  .17  millimeter,  which  pass  a  sieve  of  100  meshes  to  the  inch, 
made  of  wire  .0043"  in  diameter.  It  is  always  possible  to  exclude 
the  coarser  grams,  but  it  is  not  so  easy  to  get  rid  of  the  material 
which  is  too  fine. 

Sands  are  differentiated  into  various  sizes  by  means  of  sieves 
somewhat  arbitrarily  made,  but  so  selected  for  use  in  the  asphalt 
industry  that  the  average  diameter  of  the  particles  shall  bear  a 
definite  relation  to  each  other.  The  finest  sieve  in  use,  200  meshes 
to  the  inch,  made  of  wire  .00235"  in  diameter,  passes  particles  of 
all  degrees  of  fineness  up  to  a  diameter  of  .10  to  .083  millimeter. 
The  coarsest  parti  les  passed  by  this  sieve  are  plainly  sand  and  are 
generally  round  and  usually  undesirable.  The  next  sieve  in 
use  has  100  meshes  to  the  lineal  inch  and  is  made  of  wire  .0043" 
in  diameter.  It  passes  particles  having  a  diameter  of  about 
.17  millimeter,  or  double  that  of  those  passing  the  200-mesh  sieve. 
The  next,  made  of  wire  .00575"  with  80  meshes,  passes  particles 
of  a  diameter  of  .23  to  .24  millimeter,  three  times  that  of  the  200; 


60 


THE    MODERN    ASPHALT   PAVEMENT. 


the  next,  made  of  wire  .0090"  in  diameter,  50  meshes,  particles 
of  about  .37  millimeter,  or  four  times  the  finest  sieve.  The  40- 
mesh  sieve,  made  of  wire  .01025",  however,  passes  at  a  jump  to  a 
particle  six  times  the  diameter;  the  30,  made  of  wire  .01375" 
in  diameter,  to  one  of  eight  times;  the  20,  made  of  wire  .01650" 
in  diameter,  to  one  of  about  twelve,  and  the  10,  made  of  wire 
.027"  in  diameter,  to  one  of  about  twenty  to  twenty-five  times 
the  diameter  of  the  largest  grain  passing  the  finest  sieve.  A  more 
minute  differentiation  than  this  of  the  size  of  the  sand  grains 
would  be  burdensome  and  of  no  advantage.  For  this  reason 
sieves  of  150,  90,  70,  and  60  meshes  to  the  inch  are  not  used  in  the 
paving  industry.  As  an  example  of  the  use  of  these  sieves  the 
great  difference  between  the  size  of  the  particles  of  a  sand  suitable 
for  hydraulic  concrete  and  that  suitable  for  an  asphalt  surface 
mixture  will  serve  and  is  seen  to  be  quite  marked.  In  the  former 
a  coarse  sand  is  sought,  in  the  latter  a  fine  one. 


Hydraulic 
Concrete  Sand. 

Paving  Sand. 

Passin 

tt 
« 

g  200-mesh  sieve  ... 

Trace 

1% 
2 
,17 
18 
24 
22 
16 

100 

17% 
17 
30 
13 
10 
8 
5 

100 

100-     '        "    

80-     '        "   

50-     '        "    

40-     '        "    

30-     '        "    

20-     '        "    

10-    "        "    

It  will  be  observed  in  the  above  siftings  that  the  results  are 
Btated  in  percentages  of  the  material  passing  the  various  sieves. 
This  method  of  statement  is  much  to  be  preferred  to  that  in  which 
the  percentages  remaining  on  the  different  sieves  are  given,  and  for 
two  reasons.  In  the  first  place  it  enables  one  to  judge  of  the 
size  of  the  grains  from  the  diameter  of  the  meshes  and  the  size 
of  the  particles  passed  by  such  a  mesh,  which  cannot  be  done 
from  the  percentage  remaining  on  the  sieve.  In  the  second 
place,  as  will  appear  from  the  description  of  the  method  of  making 
a  sifting  in  Chapter  XXVIII,  it  is  much  more  easy  to  remove  the 


THE    MINERAL    AGGREGATE. 


61 


fine  material  which  passes  the  200-mesh  sieve  by  attrition  of  the 
coarser  grains  one  upon  another  and  upon  the  cloth  of  the  sieve 
than  to  separate  out  the  coarser  grains  first  and  afterwards  weigh 
the  remaining  200-mesh  material,  especially  as  there  is  apt  to 
be  a  loss  of  this  material  during  the  process  of  sieving,  which 
makes  no  difference  if  it  is  sifted  out  first  and  the  amount  deter- 
mined by  loss. 

The  sieves  which  are  used  for  the  sifting  are  carefully  made  in 
large  lots  by  one  firm  from  the  same  lot  or  roll  of  cloth  woven 
for  the  purpose,  so  that  several  sets  shall  be  so  nearly  alike  as  to 
give  uniform  results  even  in  different  hands. 

COMPARISON  OF  THE  SIEVING  OF  TWO  SAMPLES  OF  SAND 
ON  DIFFERENT  SETS  OF  SIEVES  IN  DIFFERENT  LABO- 
RATORIES. 


Sample  number  

1 

2 

Siftings     

Lab.  No.  1 

Lab.  No.  2 

Tab.  No.  1 

Lab.  No.  2 

Passing  200-mesh  sieve 

15% 

15% 

10% 

10.5% 

100- 

25 

25 

15 

18.9 

80- 

12 

12 

17 

10.5 

50- 

28 

26 

33 

34.7 

"         40- 

8 

11 

10 

11.5 

30- 

5 

5 

5 

6.3 

"         20- 

5 

5 

6 

3.2 

"         10- 

2 

1 

4 

3.1 

100 

100 

100 

98.7 

While  the  agreement  in  the  siftings  obtained  with  sieves  made 
in  this  way  is  as  concordant  as  could  be  expected  a  similar  agree- 
ment will  not  be  found  among  sieves  obtained  from  different 
sources,  especially  in  the  case  of  the  finer  ones  with  80,  100,  and 
200  meshes  to  the  linear  inch.  In  explanation  of  the  difference 
in  the  character  of  the  cloth  woven  by  the  different  manufacturers 
Messrs.  Howard  &  Morse,  of  Brooklyn,  N.  Y.,  who  manufacture 
the  sieves  in  use  by  the  author,  have  the  following  to  say  in  reply 
to  certain  questions  which  were  propounded  to  them. 

In  reply  to  the  inquiry  as  to  where  the  cloths  in  use  for  making 
these  sieves  are  manufactured  they  state  that: 


62  THE   MODERN    ASPHALT    PAVEMENT. 

"Wire  cloth  of  iron,  steel,  brass,  or  copper,  from  the  coarsest 
to  No.  100  mesh,  is  made  in  this  country,  while  the  finer  meshes 
are  imported  from  France,  Germany,  and  Scotland.  We  think 
the  Scotch  cloth  is  the  best.  Even  100  mesh  can  be  imported  at 
a  lower  cost  than  the  rate  paid  our  weavers  will  allow  it  to  be 
produced.  .  .  .  We  do  not  believe  any  American  manufacturer  could 
be  induced  to  make  the  necessary  outlay  to  produce  cloth  finer 
than  120,  unless  the  field  for  its  usefulness  was  very  much  enlarged, 
as  the  imported  cloth  at  a  much  lower  cost  seems  to  answer  every 
general  purpose  for  which  such  cloth  is  used.  Moreover  it  might 
be  necessary  to  import  the  workmen/7 

As  regards  the  process  of  manufacture  they  say: 

"Beginning  with  wire,  say,  &"  in  diameter,  the  mill  draws 
down  to  smaller  sizes  until  too  hard  to  safely  draw  smaller;  it 
is  then  annealed,  when,  its  ductility  being  restored,  it  is  drawn 
down  finer,  and  then  reannealed,  and  the  process  repeated  until 
the  requisite  size  is  obtained  and  it  is  given  its  final  annealing, 
to  render  it  fit  for  fabrication  into  cloth.  The  wire  is  delivered 
by  the  mill  to  the  wire-cloth  manufacturers  in  skeins,  which  are 
rewound  on  spools  according  to  the  mesh  required.  Usually  the 
process  is  as  follows: 

"Take  for  instance  100  mesh.  We  desire  to  put  on  a  'warp' 
say  36"X300  feet.  This  will  make  3  'cuts'  each  100  feet  long. 
We  estimate  the  weight,  allowing  for  waste  and  'thrums/  and 
taking  a  little  over  one-half  the  total  weight,  we  divide  this  as 
equally  as  we  may  among  the  100  spools,  being  careful  that  none 
are  under  weight.  The  spools  are  placed  in  a  rack  as  closely  as 
convenient;  the  wires  from  each  spool  are  led  through  a  device 
which  prevents  their  crossing  (and  serves  other  purposes  of  a 
nature  somewhat  complicated  to  explain)  to  the  'back-beam  of 
loom.7  The  100  wires  are  what  we  term  an  inch.  They  are 
tied  together  at  the 'end  and  hook  over  a  bolt-head  in  a  slot  which 
runs  lengthwise  of  the  beam,  which  in  our  looms  is  about  5' 
circumference  and  52"  long.  For  36"  width  we  hook  our  first 
inch  on  peg  18"  from  centre.  For  300  feet  we  would  need  to  put  on 
60  'rounds,'  i.e.,  the  beam  (which  is  really  a  heavy  hollow  cylinder) 
is  turned  60  times,  and  the  'lease'  wire  separating  the  contigu- 


THE    MINERAL    AGGREGATE.  63 

ous  wires  alternately  above  and  below  is  put  in  place  and  the 
beam  turned  up  one  more  revolution  to  allow  for  distance  from 
back-beam  to  face  of  loom. 

"The  inch  is  then  secured  to  another  peg,  which  is  firmly 
secured  in  the  partition  between  the  inches,  these  partitions  form- 
ing 'grooves '  in  which  the  wires  lay,  and  the  bunch  of  100  wires 
is  then  cut  off  and  the  second  groove  receives  its  60  rounds,  and  so 
continued  till  the  36  grooves  or  inches  are  filled.  This  is  a  slow, 
tedious  process. 

"However  careful  may  be  the  windings  of  the  spools,  whatever 
device  may  be  used  for  spool  racks,  yet  the  wire  will  catch  and 
break,  and  it  is  necessary  to  repair  every  break  before  another 
round  is  turned  up  on  the  back-beam.  If  the  spools  run  too  freely, 
the  wire  comes  off  too  fast,  and  a  *  bight '  will  draw  into  a  kink 
and  snap  even  with  comparatively  heavy  wires,  or  the  bight  will  lay 
across  other  wires  and  catching  may  snap  a  dozen  or  more.  How- 
ever, the  warp  being  on  the  back-beam,  one  inch  is  taken  off  the 
peg,  and  the  wires,  being  separated  by  the  '  lease/  are  passed  each 
one  in  the  order  in  which  it  lies  in  the  grooves,  first  through  the 
'gears/  or  'heddles/  and  next  through  the  'reed.'  The  heddles 
consist  of  two  frames  about  8  to  10  inches  high  by  the  width  of 
the  loom  in  length,  secured  in  a  variety  of  ways;  to  these  frames 
are  attached  twisted  wires  with  an  eye  in  the  centre.  For  100  mesh 
each  frame  must  contain  at  least  50  of  these  twisted  wires  to  each 
mesh.  The  100  wires  we  have  loosed  from  the  back-beam  are  passed 
in  their  exact  order  alternately  through  back  and  front  gear,  or 
rather  50  are  passed  through  the  eyes  of  the  back-gear  and  the  other 
50  passed  between  the  wires  of  the  back-gear  through  the  eyes  of 
the  front. 

"These  gears  being  operated  by  treadles,  it  is  evident  that 
when  the  back-gear  is  down  and  the  front  one  is  up  from  the  normal 
line  in  which  wires  would  tend  to  lie,  that  a  '  shade, '  or  shed,  is 
formed,  every  alternate  wire  being  in  the  upper,  while  the  others 
are  in  the  lower  shade,  or  shed.  The  shade  at  the  gears  may  be 
3",  while  at  the  face  of  the  cloth  it  is  nil,  and  in  front  of  the  reed 
when  swung  back  as  far  as  the  lay  will  carry  it  may  be  2".  The 
lay,  or  '  beater, '  is  hung  overhead  and  is  provided  with  a  groove 


64  THE   MODERN   ASPHALT   PAVEMENT. 

in  what  is  known  as  the  bottom  shell,  and  also  in  the  top  shell, 
which  is  removable  and  adjustable  vertically  to  suit  reeds  of  various 
heights,  which  are  so  placed  in  the  shells  as  to  have  free  lateral 
play,  but  very  little  in  any  other  direction.  All  the  inches  being 
successively  passed  through  the  gears  and  reed,  they  are  properly 
fastened  to  a '  sacking '  which  leads  from  the  face  of  the  reed  around 
a  '  breast-beam '  down  to  the  '  cloth-beam/  on  which  it  is  wound  up 
as  the  cloth  is  made. 

"The  reed  consists  of  a  series  of  '  splits '  made  of  flat  steel  of  pecul- 
iar temper.  In  a  100-mesh  reed  they  would  probably  be  about 
&"  wide,  and  the  thickness  of  each  split  would  be  equal  to  a  trifle 
less  than  the  space  between  the  wires  of  the  cloth.  They  are 
compacted  into  reeds  by  a  process  of  lacing,  which  must  be  very 
particularly  done,  as  the  split  must  stand  square  to  plane  of  cloth,, 
parallel,  and  evenly  spaced,  the  spaces  being  a  trifle  more  than  the 
thickness  of  the  wire  which  passes  through  them  and  there  must 
be  exactly  100  in  each  and  every  inch.  The  warp  being  already 
to  commence  weaving,  the  weaver,  stepping  on  the  treadle,  opens 
his  shade  and  throws  his  shuttle  through,  catching  it  on  the  other 
side  of  the  piece,  the  lay  is  brought  up  one  blow  and  he  changes 
his  treadle  and  gives  a  second  blow  to  place  the  shot.  After  throw- 
ing 100  shots  and  giving  200  blows  he  has  completed  1  inch,  when 
he  proceeds  to  count  it  and  thus  discover  whether  he  is  driving  the 
'  woof, '  or  '  filling, '  up  too  hard  or  too  lightly  to  place  100  trans- 
verse wires  in  1  inch. 

"Until  fairly  started  his  warp-wires  will  be  constantly  break- 
ing in  fine  cloth,  and  it  is  a  constant  contest  of  patience,  with 
unavoidable  delays,  until  the  last  shot  is  thrown,  though  always 
worse  at  the  beginning  and  gradually  diminishing.  After  2  or  3 
inches  have  been  made  the  weaver  gets  the '  blow  'necessary  to  secure 
the  required  fineness  in  the  mesh,  and  many  become  very  expert  and 
exact;  that  is,  we  thought  it  was  exact  until  Mr.  Richardson  called 
our  attention  to  many  inaccuracies  and  defects.  Being  as  good 
(perhaps  better)  than  similar  work  from  other  factories,  it  sold 
and  we  heard  no  complaint  of  inequalities  until  this  cement  testing 
question  brought  us  face  to  face  with  a  different  problem." 

The  size  of  the  wire  with  which  any  cloth  is  made  will  of  course 


THE    MINERAL    AGGREGATE. 


65 


have  a  decided  influence  on  the  width  of  the  meshes  of  the  cloth 
for  any  given  number  per  lineal  inch.  Messrs.  Howard  &  Morse 
state  that  while  cloth  of  the  same  mesh  can  be  made  of  many 
different  sizes  of  wire,  as  shown  for  the  coarser  sieves  by  the  ordinary 
trade  catalogues,  the  difference  is  more  theoretical  than  practical 
when  we  go  beyond  the  60-  or  70-mesh  sieves.  For  the  four  finer 
sieves  in  use  in  the  asphalt-paving  industry  the  diameter  of  the 
wire,  the  mesh,  and  the  space  between  the  meshes  are  intended  to 
be  as  follows: 


Mesh. 

Mesh. 

Diam.  of 
Wire. 

Space. 

No.    50 
"      80 
"    100 
"    200 

No.  35  O.  E.  gauge  wire.  .  . 
"    38     "         "       "    ... 

"  40    "      "     •••*'; 

"    42JB.  &  S.  wire  

.02 
.0125 
.01 
.005 

.009 
.00575 
.0043 
00235 

.011 
.00675 
.0055 
00265 

In  reply  to  the  question  as  to  why  the  ordinary  cloth  is  much 
more  regular  in  the  number  of  meshes  to  the  inch  in  the  one  direc- 
tion than  it  is  in  the  other  the  makers  of  the  sieves  say: 

"If  the  reed  be  exact  the  cloth  must  have  the  proper  number 
of  holes  one  way,  as  it  is  governed  by  the  reed.  The  reason  that 
cloth  sometimes  has  fewer  holes  the  other  way  is  that  it  is  governed 
by  the  blow  given  by  the  weaver.  If  he  can  pass  coarse  cloth 
under  the  eye  of  the  inspector,  he  gains  the  few  missing  shots  in 
each  inch  and  the  same  number  of  blows  may  in  a  day's  work  gain 
him  5  to  10  per  cent  more  pay,  but  it  is  not  so  often  the  intention 
of  the  weaver  so  to  deceive.  A  warp  of  100  may  be  put  on  the  loom 
in  December  and  not  be  out  until  the  following  June.  It  is  slow 
work.  Consider  the  effects  of  various  temperatures  and  other 
causes  which  may  affect  a  man's  disposition  meanwhile.  Too  gay 
or  cheerful,  you  would  be  obliged  to  check  his  blow  which  would 
drive  cloth  too  fine.  In  brisk,  cool  weather  cloth  would  be  driven 
up  finer  than  in  warm,  uncomfortable  weather.  Again,  a  fresh 
start  in  the  morning  means  better  cloth  than  that  made  in  the 
later  hours  of  the  day.  We  have  been  accustomed  to  pass  a  coarse- 
ness not  exceeding  5  per  cent;  i.e.,  we  would  accept  80X76  as  a 
square  mesh.  Again,  the  wire  is  not  even  in  either  temper  or  size. 


66  THE   MODERN    ASPHALT   PAVEMENT. 

Hard  wire  or  wire  a  trifle  larger  than  it  should  be  will  not  'go 
to  place'  with  the  same  blow  that  soft,  proper  gauge  wire  would 
require.  We  select  all  wire  as  carefully  as  possible,  and  though 
a  great  difference  is  not  common  in  a  single  skein,  yet  the  writer 
has  gauged  a  skein  of  brass -wire  which  has  shown  a  full  size  dif- 
ference when  gauged  at  both  ends.  Not  being  wire-drawers,  we  are 
at  a  loss  to  account  for  this.  It  seems  almost  impossible  that  a 
die  should  be  worn  so  perceptibly  in  drawing  less  than  a  mile  of 
wire,  and  yet  one  end  of  the  skein  may  be  round  while  the  other 
is  elliptical  in  cross-section.  These  causes  and  others  all  tend 
to  an  irregularity  of  mesh  which  shows  that  the  weaver  is  not 
entirely  at  fault. 

"To  eliminate  any  question  of  nicety  of  touch  and  skill  on  the 
part  of  the  weaver,  fortunes  have  been  sunk  in  experiments  to  pro- 
duce an  automatic  loom;  but  the  other  causes  remain,  and  though 
they  affect  the  accuracy  to  a  less  degree  in  a  power  loom,  yet 
they  have  a  strong  influence.  We  have  power  looms  that  will 
make  the  cloth  exact,  but  cannot  use  them  for  anything  finer  than 
20  or  30  mesh,  and  with  only  a  medium-weight  wire.  Another  cause 
that  may  affect  the  mesh  is  the  inequality  of  'temper/  or  in 
other  words,  speaking  of  other  metal  than  steel,  we  should  per- 
haps say,  'malleability/  hardness,  or  softness,  but  we  have  come 
to  use  the  word  '  temper/  however  incorrect  it  may  be,  in  reference 
to  all  metals  used  in  fabrication  of  wire  cloth. 

"The  degree  of  heat  to  which  wire  is  subjected  in  the  anneal- 
ing process  may  vary  with  the  different  charges;  more  than 
this,  it  may  vary  with  the  heat  applied  to  the  different  skeins  in 
a  single  charge,  and  more  troublesome  still,  it  may  be  hotter  on 
one  side  of  the  skein  than  on  the  other.  This  makes  serious  in- 
equalities in  the  'temper'  and  in  consequence  a  variation  in  the 
mesh  of  the  cloth  in  which  it  is  to  be  used." 

Messrs.  Howard  &  Morse  also  add  as  a  reason  for  the  great 
variability  in  the  sieves  offered  by  the  trade: 

"That  each  wire-cloth  manufacturer  has  ideas  of  his  own 
as  to  what  the  trade  requires:  for  instance,  he  may  use  48  reed 
for  50  mesh  and  have  his  cloth  driven  up  to  44  the  other  way, 
so  that  he  will  furnish  you  on  your  call  for  50  mesh  a  piece  48X44, 


THE    MINERAL    AGGREGATE.  67 

while  the  manufacturer  who  gave  you  50X50  on  your  call  gives 
you  a  cloth  that  costs  him  more,  both  for  material  and  labor  than 
the  other. 

"Again,  certain  trades,  notably  the  paper  trade,  requires  cloth 
not  driven  up  square,  and  48x38  passes  for  50  mesh,  68x52  for 
70  mesh,  and  if  this  cloth  passes  through  other  channels,  as  a  dealer's 
hands,  he  will  sell  a  piece  to  any  transient  customer,  say  58X46. 
and  call  it  60  mesh,  and  with  entire  innocence,  for  he  bought  it  for 
60  mesh. 

"Mill  strainer  cloth  is  another  irregularity.  It  is  made  of 
very  light  wire  and  not  driven  up  with  any  approach  to  accu- 
racy. In  fact  the  low  price  obtained  for  it  prohibits  care  in  its 
manufacture.  It  is  either  woven  by  boys  or  on  a  power  loom, 
which,  as  explained  above,  will  not  insure  accuracy  in  fine  meshes." 

The  Committee  on  Uniform  Tests  of  Portland  Cement  of 
the  American  Society  of  Civil  Engineers  at  one  time  hoped  that 
all  sieves  in  use  in  the  testing  of  cement  might  be  constructed 
of  wire  the  diameter  of  which  should  be  one-half  the  width  of  the 
opening.  If  sieves  could  be  constructed  on  this  plan  it  would 
no  doubt  be  very  desirable,  but  in  response  to  an  inquiry  as  to 
whether  this  could  be  done  the  manufacturers  make  the  following 
statement  : 

"To  make  fine  brass  cloth  with  the  diameter  of  wire  one-half 
the  width  of  opening  would  result  in  a  flimsy  fabrication  which  in 
use  would  give  you  more  unsatisfactory  results  than  you  now 
attain. 

"The  individual  wires  would  be  of  very  little  use  and  not  only 
break  very  easily,  but  would  push  to  one  side  or  the  other;  two  con- 
tiguous wires  crowding  each  the  neighboring  wire  would  separate 
and  give  space  four  times  the  size  natural  to  the  mesh.  We  find 
that  in  order  to  make  a  fairly  rigid  cloth  it  is  necessary  that  the 
diameter  of  wire  be  about  80  per  cent  of  space  size,  or  practically 
as  shown  in  table  on  page  65.  To  make  the  lighter  wire  would 
increase  cost,  though  we  presume  that  is  of  minor  importance,  and 
yet  it  must  be  considered.  It  would  be  difficult  to  make  this  per- 
fectly clear  perhaps.  To  take  a  sample  case  of  frequent  occur- 
rence: Our  customers  know  that  in  the  coarse  grades  of  cloth 


68  THE    MODERN    ASPHALT   PAVEMENT.       . 

for  a  certain  mesh  the  price  diminishes  as  diameter  of  wire 
decreases,  and  this  is  true  up  to  about  60  mesh.  We  make  this 
from  stock  of  No.  36  O.  E.  gauge  wire  (.0075").  They  order  No.  37 
in  hope  of  obtaining  it  at  a  lower  price  per  square  foot.  The 
weight  of  60  of  No.  37  is  75£  per  cent  as  great  as  the  weight  of  60  of 
36 ;  and  yet  material  for  37  costs  about  40  per  cent  more  per  pound 
than  36.  This  difference  becomes  greater  as  we  advance  to  the 
finer  sizes.  No.  200  mesh  is  made  of  .00235"  wire  (as  near  as  the 
micrometer  gauge  will  show  it).  The  finest  wire  the  writer  ever 
saw  was  silver  .002"  in  diameter,  and  this  was  shown  as  a  curiosity 
rather  than  of  any  practical  use. 

"It  may  be  that  the  ductility  of  brass  is  sufficient  to  make 
it  practicable  to  draw  it  to  .0017",  but  we  doubt  it,  and  at 
what  expense?  105,263'  to  one  pound,  i.e.,  to  draw  one  pound 
.0017"  brass  wire  about  20  miles  of  wire  must  pass  through  the 
dies.  This  is  getting  down  to  fine  work.  It  means  about  sixteen 
days'  work  to  one  pound,  and  the  finer  the  wire  the  more  slowly 
it  must  be  drawn.  We  do  not  mean  weight,  for  that  is  evident, 
but  as  regards  length.  Imagine,  too,  the  making  of  the  die.  Can 
one  expect  it  to  be  round,  square,  or  true  to  any  regular  shape, 
or  exactly  accurate  with  regard  to  size? 

"Take  even  our  80  mesh,  the  wire  wherein  is  .00575"  in  diame- 
ter, nearly  3£  times  the  diameter  of  the  wire  you  specify  for  the 
200  mesh,  11 J  times  as  large  in  area  of  cross-section,  consequently 
11£  times  as  heavy  in  a  given  length,  and  contemplate  the  skill 
required  to  make  a  hole  in  a  die  which  shall  be  round  and  with 
an  exact  diameter  smaller  than  the  hole  in  100-mesh  cloth.  Con- 
sider the  care  necessary  in  drawing  this  wire,  constant  watching 
to  note  when  the  die  is  worn  too  large,  and  the  whole  manipulation 
until  wire  is  woven  into  cloth  and  put  into  sieves,  and  there  will 
be  apparent  reasons  sufficient  for  the  inaccuracies  noted  by  you 
from  time  to  time. 

"Up  to  100  mesh  we  can  make  a  cloth  as  accurate  as  any  one 
in  the  trade;  beyond  that  we  cannot  control  it.  We  will  write 
parties  in  Glasgow  in  a  few  days,  and  if  we  can  learn  any- 
thing of  interest  to  you  will  be  glad  to  communicate  it  to 
you. 


THE    MINERAL    AGGREGATE.  69 

'•'We  are  willing  to  put  on  a  short  warp,  say  36"X  100  feet  each 
Nos.  50,  80  and  100  mesh,  guaranteeing  that  it  shall  be  driven 
up  square,  i.e.,  the  50  to  between  48  and  50,  and  the  80  between 
77  and  80,  and  the  ICO  to  between  97  and  101,  the  wire  carefully 
selected  to  conform  to  size  given  in  answer  to  No.  5  (see  table 
on  page  65),  within  2  per  cent  of  diameter,  provided  you  will 
agree  to  find  sale  for  same,  at  list  price  net,  within  one  year  of 
completion. 

"We  are  aware  that  we  are  undertaking  a  hard  piece  of  work. 
The  delays  will  be  expensive;  we  shall  expect  to  pay  more  than 
the  usual  price  for  the  wire;  every  skein  will  need  to  be  gauged 
at  both  ends,  and  if  long,  in  the  centre  as  well;  much  of  the  wire 
will  have  to  be  discarded;  the  mill  contests  our  claims  of  inaccuracy; 
the  cloth  will  have  to  be  carefully  and  constantly  watched,  and 
the  supervision  will  be  onerous,  but  we  are  desirous  of  giving 
you  all  the  satisfaction  possible,  though  naturally  without  pecuniary 
loss  to  ourselves,  and  we  therefore  do  not  consider  the  whole 
cost  of  supervision  in  naming  the  above  price. " 

The  preceding  explanation  will  enable  the  reader  to  grasp  the 
difficulty  of  obtaining  satisfactory  sieves  more  readily  than  any- 
thing that  could  be  said  by  the  author,  and  it  will  show  the  care 
which  is  used  in  order  to  obtain,  for  use  in  the  asphalt  industry, 
sieves  which  are  at  least  uniform  among  themselves  and  which 
can  be  considered  as  standards,  at  least  arbitrarily  if  not  abso- 
lutely.* 

That  a  better  grade  of  2CO-mesh  cloth  can  be  obtained  which 
is  much  more  regular  than  the  average  supply  can  be  seen  from 
the  accompanying  illustration,  Fig.  3,  where  the  good  can  be  dis- 
tinguished from  the  poor  cloth  without  difficulty,  and  where  it 
can  be  seen  that  the  lack  of  regularity  is  due  to  the  manner  in 
which  the  weaver  pushes  up  the  wire. 

Until  1907,  the  200-mesh  cloth  was  twilled,  but  since  that 
time  Messrs.  Howard  &  Morse  have  produced  a  plain  woven  cloth, 
which  in  some  ways  is  more  satisfactory  as  far  as  the  number  of 
mashes  per  inch  is  concerned,  but  will  probably  not  wear  as  well 
as  the  twilled  material.  Three  counts  of  this  cloth  recently  made, 
resulted  as  follows : 


70  THE  MODERN  ASPHALT  PAVEMENT. 

Warp.  Woof. 

First  piece 200  197 

Second  piece 200  197 

Third  piece 200  198 

while  the  100-mesh  cloth  made  at  the  same  time  with  great  care 
counted 

Warp.  Woof 

First  piece 100  98 

Second  piece 100  102 

These  counts  are  much  more  satisfactory  than  those  which 
were  formerly  obtained. 


Good  Cloth.  Poor  Cloth. 

FIG.  3. 

The  sieves  are  generally  known,  as  has  appeared  in  what  has 
been  said,  by  the  number  of  meshes  which  they  show  to  the  linear 
inch.  For  strictly  scientific  purposes  they  would  be  more  properly 
identified  by  the  diameter  of  the  largest  particle  which  each  sieve 
would  pass,  and  these  diameters  have  already  been  given  for  the 
sieves  which  are  in  use  in  the  asphalt  industry.  For  the  purpose 
of  determining  this  diameter  Mr.  Allen  Hazen  adopted  a  method 
which  he  describes  as  follows:1 


twenty-fourth  Annual  Report  of  the  State  Board  of  Health  of  Mas- 
sachusetts, 1892,  541. 


THE    MINERAL   AGGREGATE.  71 

"It  can  be  easily  shown  by  experiment  that  when  a  mixed 
sand  is  shaken  upon  a  sieve  the  smallest  particles  pass  first,  and 
as  the  shaking  is  continued  larger  and  larger  particles  pass,  until 
the  limit  is  reached,  when  almost  nothing  will  pass.  The  last  and 
largest  particles  passing  are  collected  and  measured,  and  they 
represent  the  separation  of  that  sieve.  The  size  of  separation  of 
a  sieve  bears  a  tolerably  definite  relation  to  the  size  of  the  mesh, 
but  the  relation  is  not  to  be  depended  upon,  owing  to  the  irregu- 
larities in  the  meshes  and  also  to  the  fact  that  the  finer  sieves 
are  woven  on  a  different  pattern  from  the  coarser  ones,  and  the 
particles  passing  the  finer  sieves  are  somewhat  larger  in  proportion 
to  the  mesh  than  is  the  case  with  the  coarser  sieves.  For  these 
reasons  the  sizes  of  the  sand  grains  are  determined  by  actual 
measurements  regardless  of  the  size  of  the  mesh  of  the  sieve.  .  .  . 

"The  sizes  of  the  sand  grains  can  be  determined  in  either  of 
two  ways:  from  the  weight  of  the  particles  or  from  micrometer 
measurements.  For  convenience  the  size  of  each  particle  is  con- 
sidered to  be  the  diameter  of  a  sphere  of  equal  volume.  When 
the  weight  and  specific  gravity  of  a  particle  are  known,  the  diameter 
can  be  readily  calculated.  The  volume  of  a  sphere  is  fad3,  and 
is  also  equal  to  the  weight  divided  by  the  specific  gravity.  With 
the  Lawrence  materials,  the  specific  gravity  is  uniformly  2.65 
within  very  narrow  limits,  and  we  have 


Solving  for  d  we  obtain  the  formulae 


when  d  is  the  diameter  of  a  particle  in  millimeters  and  w  its  weight 
in  milligrams.  As  the  average  weight  of  particles  when  not  too 
small  can  be  determined  with  precision,  this  method  is  very  accu- 
rate, and  altogether  the  most  satisfactory  for  particles  above 
.10  millimeter;  that  is,  for  all  sieve  separations.  For  the  finer 


72  THE  MODERN  ASPHALT  PAVEMENT. 

particles  the  method  is  inapplicable,  on  account  of  the  vast  num- 
ber of  particles  to  be  counted  in  the  smallest  portion  which  can 
be  accurately  weighed,  and  in  these  cases  the  sizes  are  determined 
by  micrometer  measurements.  As  the  sand  grains  are  not  spher- 
ical or  even  regular  in  shape,  considerable  care  is  required  to  ascer- 
tain the  true  mean  diameter.  The  most  accurate  method  is  to 
measure  the  long  diameter  and  the  middle  diameter  at  right  angles 
to  it,  as  seen  by  a  microscope.  The  short  diameter  is  obtained 
by  a  micrometer  screw,  focusing  first  upon  the  glass  upon  which 
the  particle  rests  and  then  upon  the  highest  point  to  be  found. 
The  mean  diameter  is  then  the  cube  root  of  the  product  of  the  three 
observed  diameters.  The  middle  diameter  is  usually  about  equal 
to  the  mean  diameter,  and  can  generally  be  used  for  it,  avoiding 
the  troublesome  measurement  of  the  short  diameters. 

"The  sizes  of  the  separations  of  the  sieves  are  always  deter- 
mined from  the  very  last  sand  which  passes  through  in  the  course 
of  an  analysis,  and  the  results  so  obtained  are  quite  accurate." 

Voids  in  Sand. — Sand  consists  of  particles  of  such  shapes  that 
they  cannot  be  packed  in  any  space  without  leaving  intervals 
between  the  grains  which  are  not  filled.  These  spaces  are  known 
as  voids  and  their  volume  and  the  size  of  the  spaces  are  very  impor- 
tant in  characterizing  different  sands.  The  amount  of  volume 
of  the  voids  and  their  size  are  dependent  on  the  shape  and  variety 
in  the  size  of  the  grains,  upon  the  way  they  are  arranged,  and  upon 
the  degree  to  which  they  are  compacted.  If  the  sand  grains  were 
perfect  spheres  it  can  be  regularly  calculated  what  the  percentage 
of  voids  in  any  volume  will  be.  Dr.  G.  F.  Becker,  of  the  United 
States  Geological  Survey,  has  made  this  calculation  for  me  and 
states  the  results  as  follows: 

"Suppose,  first,  that  8  spheres  of  radius  r  are  so  arranged  that 
the  centre  of  each  is  at  one  corner  of  a  cube  and  that  the  edge 
of  the  cube  is  2r.  Then  one-eighth  of  each  sphere  will  be  included 
within  the  cube,  and  the  total  of  the  spherical  matter  in  the  cube 
will  be  just  one  sphere.  In  this  case  the  voids  will  be 


THE    MINERAL    AGGREGATE. 


73 


"Now  shift  the  four  spheres  forming  the  lower  layer  into  this 
order 


which  amounts  to  changing  the  angles  made  by  the  edges  of  the 
cube  without  any  change  in  length.  Also  bring  the  centres  of 
the  upper  layer  of  spheres  over  the  point  marked  "x".  Then 
the  cube  is  distorted  into  an  oblique  prism  of  which  this  is  a  plan. 


"It  still  includes  just  one  sphere. 
face  of  the  prism  will  be 


The  area  of  the  lower  BUT- 


74  THE  MODERN  ASPHALT  PAVEMENT. 


and  the  height  of  the  prism  is  the  height  of  a  tetrahedron  formed 
by  the  centres  of  four  spheres  when  three  are  placed  in  contact 
in  one  plane  and  the  fourth  is  laid  upon  them.  This  height,  and 
thus  the  whole  volume  of  the  prism,  is 


and  the  interstitial  space  is 

-  =  1 ^==0.2595 

4v/2r3  3\/2 

"By  diminishing  all  lines  in  one  direction  in  the  same  propor- 
tion the  system  of  spheres  becomes  a  system  of  ellipsoids.  Since 
the  spheres  and  the  interstitial  spaces  are  distorted  in  the  same 
manner,  it  is  evident  that  a  system  of  equal  and  similarly  oriented 
ellipsoids  may  also  be  packed  so  as  to  leave  only  25.95  per  cent 
of  voids.  But  if  any  ellipsoid  is  differently  oriented  from  the  rest, 
the  voids  will  be  greater." 

With  the  spheres  or  regularly  oriented  ellipsoids  packed  as 
closely  as  possible  the  voids  should  therefore  be  25.95  per  cent, 
but  it  is  not  possible  to  pack  small  grains  like  sand  in  this  regular 
way.  They  are  jumbled  together  irregularly,  and  experiment  has 
shown  that  perfect  spheres  like  small  bird  shot  when  shaken 
and  tamped  until  they  are  as  compact  as  it  is  practical  to  make 
them  with  the  devices  at  our  command  still  contain  voids  of  32  per 
cent,  or  6  per  cent  more  than  theory. 

With  spheres  of  quartz  of  similar  size  it  would  probably  be 
impossible  to  compact  them  to  the  same  extent,  while  if  the  material 
is  merely  poured  loosely  into  the  space  which  is  to  be  filled  and  no 
attempt  is  made  to  attain  greater  compaction  the  voids  will  be 
found  to  be  very  much  larger. 


THE    MINERAL    AGGREGATE.  75 

It  is  important  therefore  before  going  further  to  consider  the 
conditions  under  which  determinations  of  voids  are  usually  made 
and  to  decide  upon  a  uniform  method,  one  which  is  the  best  to 
use  in  obtaining  results  of  both  absolute  and  relative  value.  There 
are  several  difficulties  to  be  met  with  in  arriving  at  the  ultimate 
practical  compaction  of  sand  aside  from  the  impossibility  of  bring- 
ing small  particles  of  any  size  and  shape  into  the  closest  possible 
juxtaposition. 

Determination  of  the  Voids  in  Sand. — The  usual  method  of 
determining  voids  in  sand,  gravel,  stone,  etc.,  is  to  fill  a  vessel 
of  known  volume  with  the  material  in  the  condition  under  which 
it  is  desired  to  find  the  voids  and  then  to  pour  in  water  until  the 
space  between  the  grains  is  filled,  thus  determining  the  voids 
from  the  relation  of  the  volume  of  water  to  the  volume  occupied 
by  the  material  examined.  This  method  is  satisfactory  with 
coarse  substances  like  gravel,  but  not  when  grains  smaller  than 
those  which  will  pass  a  30-mesti  sieve  are  present.  One  reason 
why  it  is  not  satisfactory  with  fine  material  is  because  air  is  liable 
to  be  entangled  between  the  grains  and  not  to  be  replaced  by 
water.  According  to  another  method  a  definite  volume  of  the 
compacted  material  is  poured  into  a  measured  volume  of  water. 
The  increase  in  volume  is  that  of  the  material  and  the  difference  is 
that  of  the  voids.  This  is  a  more  satisfactory  way  if  no  fine  material 
or  dust  is  present,  which  has  a  tendency  to  float  in  water  or  to 
obscure  the  meniscus. 

It  is  better,  therefore,  to  determine  the  specific  gravity  of  the 
material  of  which  the  grains  are  composed  and  then  calculate 
the  voids  from  the  weight  of  a  definite  volume  of  sand.  For 
instance,  if  100  cubic  centimeters  of  quartz  sand  weighs  168 
grammes  and  the  specific  gravity  of  the  grains  is  2.65  the  voids 
may  be  found  by  dividing  the  weight  by  the  gravity  multiplied 
by  100  and  subtracting  the  results  from  100,  the  result  in  this  case 
being  100-168-^2.65  =  36.6  which  is  the  per  cent  of  voids  by  vol- 
ume in  this  sand. 

Where  the  ultimate  practical  compaction  of  fine  material  is 
sought,  some  further  precautions  must  be  taken,  as  this  cannot  be 
accomplished  at  all  at  ordinary  room  temperatures,  as  a  film  of 


76 


THE  MODERN  ASPHALT  PAVEMENT. 


adsorbed  aqueous  vapor  adheres  to  each  grain,  which  keeps  them 
apart.  With  dust  or  200-mesh  material  alone,  air  also  is  often 
imprisoned  in  the  mass  and  increases  the  voids.  If,  however,  the 
sand  or  dust  is  heated  above  the  temperature  of  boiling  water  these 
difficulties  are  removed  and  the  fine  grains  compact  as  well  as 
coarser  ones.  As  examples,  the  voids  found  'in  a  sand  and  in  a 
ground  limestone  when  determined  with  hot  and  cold  materials 
respectively  were : 

VOLUME  OF  VOIDS. 


1 

Cold. 

Hot. 

Sand  
Dust.  

34.2 
56.6 

33.3 
38.0 

In  each  determination  the  means  employed  for  compaction 
were  the  same,  but  only  when  the  material  was  hot  was  this  com- 
plete, especially  with  the  fine  dust.  The  degree  of  compaction  to 
which  a  substance  such  as  sand  is  subjected  of  course  influences 
the  extent  of  the  voids.  The  relation  between  those  in  a  mass 
loosely  poured  into  a  cylinder  and  slightly  shaken  down  but 
not  compacted  and  those  in  a  thoroughly  compacted  mass  can 
be  seen  from  the  following  determinations: 

VOIDS. 


Loosely 
Compacted. 

Thoroughly 
Compacted. 

Long  Island  sand  —  coarse  
Buffalo  —  fine  
Chicago  

41.7 
45.4 
42.2 

33.7 
37.9 
35.5 

New  Orleans  —  very  coarse  

37.6 

29.6 

Kansas  City  —  very  fine 

4G  9 

36.0 

The  voids  in  sands  and  mineral  aggregates  should  of  course 
be  determined  in  a  state  of  thorough  compaction,  as  this  is  the 
condition  in  which  these  materials  are  or  should  be  found  in  a 
finished  asphalt  surface. 


THE    MINERAL   AGGREGATE. 


77 


Weight  per  Cubic  Foot.— The  voids  being  known  in  any  sand 
or  aggregate,  and  the  gravity  of  the  particles  (for  all  practical 
purposes  for  quartz  sand  this  may  be  taken  as  2.65),  the  weight 
per  cubic  foot  is  calculated  and  is  usually  stated  together  with 
per  cent  of  voids,  as  it  is  a  factor  of  some  importance  hi  consider- 
ing the  relations  of  bitumen  to  the  aggregate  in  certain  surface 
mixtures,  sand  being  frequently  taken  by  volume — 9  cubic  feet — 
and  as  an  indication  of  possible  density  of  the  finished  surface. 

The  very  considerable  variations  in  the  voids  and  weight  per 
cubic  foot  in  various  unmixed  sands  examined  in  1894  and  later 
are  seen  in  the  following  tables,  pages  77  and  78. 

VOLUME  WEIGHTS  AND  VOIDS  IN  SANDS. 


- 

Wt.  per 
Cu  Ft. 
Loose. 

Voids. 

Wt.  per 
Cu.  Ft. 
Compact. 

Voids. 

Ballast  —  very  fine  . 

92  0 

45  4 

102  7 

37  9 

Buffalo  —  No*  3 

97  1 

41  2 

110  4 

33  2 

New  Orleans  —  Prophet  Island  —  coarse.  .  . 
'  '         screened. 
"      —  lakeshore  

103.4 
100.9 
95  1 

37.6 
39.1 
42  5 

116.4 
113.6 
109  1 

29.6 
33.3 
34  0 

1  '         '  '      —  Jordan  River  —  much  loam. 
Omaha  .  . 

82.4 
98  6 

51.2 
40  4 

95.3 
109  1 

42.4 
34  i 

London  —  coarse  

94  9 

42  6 

107  8 

34  8 

—  fine  

86  6 

44  9 

99  9 

39  6 

Yonkers  —  coarse  

94  6 

42  8 

106  6 

35  6 

"       —fine  

92  9 

43  8 

106  5 

35  6 

Chicago.  . 

95  6 

42  2 

107  7 

35  0 

Boston.  

94  0 

43  3 

106  4 

35  7 

New  York  

94.4 

43.0 

108  3 

34  6 

Kansas  City  —  fine  

87  0 

46  9 

105  9 

36  0 

'  —  coarse  

101  7 

38  5 

112  9 

31  7 

Altoona  

92  4 

44  1 

105  1 

37  7 

Youngstown  

92  4 

44  1 

105  0 

36  5 

Niagara  Falls  —  No.  1  

92.1 

44  3 

107  6 

35  0 

n          ((   <i    2 

89.4 

46  0 

99  8 

40  0 

Louisville  

91.9 

44.5 

101  6 

38  6 

Fort  Wayne 

91  4 

44  7 

108  8 

34  3 

Washington                                     ...    . 

89  2 

46  1 

100  1 

39  5 

Harrisburg  —  (much  coal)             

83.4 

97  0 

41  3 

Voids  as  Affected  by  Size  and  Shape  of  Particles  and  by  their 
Uniformity. — With  the  method  of  determining  the  voids  in  sands 
in  a  uniform  and  satisfactory  way  in  mind,  the  peculiarities  found 
in  the  aggregation  of  particles  of  mineral  matter  of  different  shape 
and  size  may  be  considered. 

Voids  in  Sand  Consisting  of  Particles  of  Uniform  Size. — If  the 


78 


THE  MODERN  ASPHALT  PAVEMENT . 


particles  of  a  sand  are  all  of  uniform  size,  or  nearly  so,  the  voids 
present  under  our  normal  conditions  will  depend  upon  the  shape 
of  the  particles  alone.  Sand  the  grains  of  which  are  perfect 
spheres  would  have,  as  has  been  noted  for  fine  shot,  voids  of 
32  per  cent,  theory  being  25.95,  whereas  irregular  fragments, 
such  as  are  found  in  crushed  stone,  the  crushed  quartz  of  the 
sand-paper  manufacturer,  contain  practically  about  44  per  cent, 
but  if  the  particles  are  uniform  their  absolute  size  has  no  influence 
on  the  volume  of  the  voids  they  show.  As  examples,  the  following 


GRADING,  POUNDS  PER  CUBIC  FOOT,  AND  VOIDS  IN  VARIOUS 
SANDS  OF  1899. 


Test 
No. 

Source. 

Passing  Mesh. 

Total. 

Retained 
on  10. 

Lbs. 
per 
Cu.Ft. 

4 
1 

200 

100 

80 

50 

40 

30 

20 

10 

22693 
22694 
22768 
22769 
22789 
22790 

22802 
22803 
22827 

22917 
22925 

22967 
22968 

Paterson,  Sand  Hill 
No.  16  

3 
4 
3 
2 
0 

23 
17 
2 

6 
2 

22 
3 
2 

9 
12 
15 
3 
2 

24 
50 
5 

20 
2 

15 
51 
13 

6 
14 
23 
3 
3 

16 

18 
7 

12 
2 

9 

28 
17 

36 
42 
56 
19 
53 

28 
13 

47 

)0 

7 

12 
16 
43 

23 

18 
3 
28 
31 

8 
2 
26 

10 
18 

8 
2 
13 

13 
8 
0 
18 
6 

1 

0 
8 

2 

20 

6 
0 
5 

5 
2 
0 
18 
3 

0 
0 
3 

0 
30 

8 

0 
4 

5 

0 
0 
9 
2 

0 
0 
2 

0 
19 

20 
0 
3 

=  100% 
=  100% 
=  100% 
=  100% 
=  100% 

=  100% 
=  100% 
=  100% 

=  100% 
=  100% 

=  100% 
=  100% 
=  100%, 

10% 

5% 

104.7 
102.2 
104.7 
97.7 
99.7 

103.4 
102.2 
107.2 

107.2 
112.1 

105.9 
99.7 
104.7 

36.6 
38.1 
36.6 
39.6 
39.6 

37.4 
36.1 
35.1 

35.1 

32.1 

35.8 
39.6 
36.6 

Paterson,  Sand  Hill 
No  17 

Scranton,  Temper- 
ing No  1. 

Scranton,  Temper- 
ing No.  2  
Louisville    No.     1  , 
coarse  

Louisville    No.     1  , 
fine  

Saginaw,fine  bank. 
Sag.  River 
La  Fayette  No.  9, 
Wagner  bank.  .  .  . 
Kansas  City,  Kaw 
River,  coarse.  .  .  . 
Washington  No.  3, 
crusher  dust 

Chicago,  fine  sand.  . 
'  '        coarse  sand 

determinations  of  voids  in  crushed  quartz  of  uniform  but  very 
varied  size  will  sieve: 


THE    MINERAL    AGGREGATE. 


79 


Crushed  Quartz  —  very  Sharp. 

Volume  Per 
Cent  of 
Voids. 

Passing  6-mesh  sieve  —  not  passing  10.  .  . 
"  20-  "  "  —  "  "  30.  .  . 
"  90-  "  "  —  "  "  100.  .  . 

43.3 
43.4 
44.2 

These  materials  represent  a  very  coarse  sand,  a  sand  of  size 
in  use  in  concrete,  and  a  very  fine  sand  but  all  of  the  particles 
of  very  uniform  size.  They  all  contain,  when  compacted  hot, 
the  same  volume  of  voids.  Without  compaction  material  of 
this  description  will,  however,  vary  hi  proportion  to  the  fineness 
of  the  particles;  a  coarse  broken  stone  of  uniform  size  will  have 
47  per  cent  of  voids,  while  a  similar  fine  sand  will  often  have  over 
50,  owing  to  the  fact  that  the  finer  material  will  not  naturally 
assume  the  same  degree  of  compaction  as  the  coarser  material. 

The  crushed  quartz,  the  voids  in  which,  when  compacted, 
have  just  been  given,  consists  of  extremely  sharp  particles  with 
the  angles  of  the  original  fracture  unworn.  In  sands  the  grains 
are  more  or  less  round  as  has  been  shown,  and  hi  consequence 
they  pack  more  readily  and  closely.  If  sands  are  taken  and  sepa- 
rated into  portions  the  particles  of  each  one  of  which  are  of  nearly 
the  same  size — that  is  to  say,  will  pass  a  certain  sieve  but  be 
retained  on  one  of  the  next  smaller  size — and  the  voids  are  deter- 
mined for  each  of  these,  it  will  be  found  that  there  is  a  very  con- 
siderable variation  hi  the  voids  for  the  same  sized  particles  of 
different  sands  and  also  for  the  different  sizes,  and  that  with  all 
of  them  the  voids  are  smaller  hi  volume  than  was  the  case  with 
the  sharp  particles  of  crushed  quartz.  Following  are  illustrations; 


80 


THE  MODERN  ASPHALT  PAVEMENT. 
SIFTING. 


Source. 

Passing  Mesh. 

Total. 

200 

100 

80 

50 

40 

30 

20 

10 

Buffalo  —  Canada  lakeshore 
Omaha  —  Platte  River,  1897 
Chicago  —  fine  lake,  1897.  .  . 
Detroit—  fine  lake,  1897.  .  .  . 
Kansas    City  —  fine    river, 
1897          '             

17 
5 
2 
2 

10 
10 
32 

24 
13 
74 
10 

15 
12 
29 

15 
34 
23 
23 

23 

8 
17 

24 
31 
1 
59 

44 
27 
19 

10 

8 

4 
3 

4 
4 

2 
2 

=  100% 
=  100% 
=  100% 
=  100% 

=  100% 
=  100% 
=  100% 

4 

6 
15 

1 

2 

1 
12 
1 

1 

7 
1 

"9" 

Long  Island  bank,  1897.  .  .  . 
Buffalo  —  Attica  fine  bank.  . 

See  also  tables  on  pages  81  and  82. 

The  crushed  quartz  of  about  the  100-mesh  size  contains  44.2 
per  cent  of  voids.  The  100-mesh  particles  of  the  fine  Attica  sand 
showed  but  42.9  per  cent  and  the  same  sized  grains  of  the  other 
sands  much  less,  until  those  from  the  coarse  Buffalo  supply  con- 
tained but  34.5  per  cent. 

Voids  in  Sand  of  Varying  Sized  Particles  or  Grains. — When  the 
grains  in  a  sand  vary  in  size  the  voids  are  at  once  reduced  in  volume 
by  the  fitting  of  the  smaller  particles  into  the  spaces  between  the 
larger  ones,  the  voids  at  the  same  tune  becoming  smaller  in  size 
as  well  as  in  volume. 


THE    MINERAL   AGGREGATE. 


81 


VOIDS. 


Source. 

Loose—  Hot. 

Entire. 

Passing  Mesh. 

200 

100 

80 

50 

Buffalo  —  Canada  lake  l 

40.3% 
35.8 
46  3 

'48.'6% 

41.8% 
43.7 
43.6 
45.8 
45.9 
49.0 
45.7 

38.3% 
42.6 
46.6 
44.0 
44.6 
48.1 
47.5 

42.0% 
42.9 
46.8 
41.3 
42.9 
47.3 
47.1 

Omaha  —  Platte  River,  1897  

Chicago  —  fine  lake,  1897  

Detroit  —  fine  lake,  1897  

41  1 

Kansas  City—  fine  river,  1897.  .  .  . 
Long  Island—  bank,  1897  
Buffalo  —  Attica,  fine  bank,  1897 

41.0 
39.2 

49.8 
50.1 
48.0 

Source. 

Tamped  —  Hot. 

Entire. 

Passing  Mesh. 

200 

100 

80 

50 

Buffalo  —  Canada  lake  *  

34.6% 
33.5 
39  2 

'44:5% 

34.5% 
38.4 
38.4 
39.6 
40.2 
41.8 
42.9 

32.8% 
37.5 
40.2 
39.1 
40.1 
43.4 
41.3 

36.5% 
37.5 
42.3 
37.5 
38.8 
42.4 
41.4 

Omaha—  Platte  River,  1897.  
Chicago  —  fine  lake,  1897  . 

Detroit  —  fine  lake,  1897. 

35  4 

Kansas  City  —  fine  river,  1897.  .  .  . 
Long  Island—  bank,  1897  
Buffalo—  Attica,  fine  bank,  1897.  . 

35.3 
33.0 
32.0 

42.7 
42.1 
37.7 

1 1.33  per  cent  magnetite. 

When  the  various  sized  particles,  the  voids  in  which  taken  sepa- 
rately are  shown  in  the  preceding  table,  are  combined  in  the  pro- 
portions found  in  nature,  the  voids  are  then,  with  one  or  two  ex- 
ceptions, much  reduced.  This  is  conspicuous  in  the  Attica  sand, 
which  as  a  whole  shows  32  per  cent  of  voids,  where  its  200  mesh 
has  37.7  per  cent  and  the  coarser  particles  over  40  per  cent. 

The  greatest  reduction  will  of  course  occur  where  there  are 
enough  fine  particles  present  of  a  size  small  enough  to  fit  between 
the  larger  ones — for  instance,  dust  with  sand,  sand  with  gravel, 
and  gravel  with  broken  stone.  It  was  found  that  by  adding  dust 


82  THE  MODERN  ASPHALT  PAVEMENT. 

VOLUME  WEIGHT  OF  HOT  SAND,   POUNDS   PER   CUBIC  FOOT. 


Source. 

Loose—  Hot. 

Tamped  —  Hot. 

Entire 

Passing  Mesh. 

Entire 

Passing  Mesh. 

100 

80 

50 

100 

80 

50 

Buffalo  —  Canada  lake  !  .  .  .  . 
Omaha—  Platte  River,  1897 
Chicago—  fine  lake,  1897.  .  . 
Detroit  —  fine  lake,  1897  
Kansas    City  —  fine    river, 
1897  

98.5 

93.'5 
97.2 

97.4 
100.3 

99.4 

96.0 
92.9 
93.1 
89.5 

89.3 
84.2 

89.6 

101.8 
94.6 
88.1 
92.5 

91.5 

85.5 

86.7 

95.6 
94.2 
87.8 
96.9 

94.3 
87.0 

87.3 

108.0 
109.7 
100.3 
106.6 

106.8 
110.8 

112.2 

108.2 
101.6 
101.6 
99.7 

98.7 
96.1 

94.2 

110.9 
103.1 
96.7 
100.6 

99.1 
94.0 

96.9 

104.8 
103.1 
95.3 
103.2 

101.1 
96.1 

96.8 

Long  Island  —  bank,  1897.  . 
Buffalo  —  Attica,  fine  bank, 
1897                 

1 1.33  per  cent  magnetite. 

in  continually  increasing  portions  to  a  sand  with  35.5  per  cent 
of  voids,  the  percentage  of  voids  in  the  mixture  was  gradually 
reduced  to  a  certain  point  corresponding  to  the  voids  to  be  filled, 
but  on  further  addition  they  were  again  increased,  as  shown  by 
the  following  figures.  This  point  was  reached  when  the  dust 
amounted  to  41  per  cent  of  the  sand,  an  amount  greater  than  the 
voids;  but  this  is  due  to  the  fact  that  the  sand  grains  were  un- 
avoidably separated  to  a  very  considerable  extent  by  the  dust  and 
the  voids  consequently  increased. 

WEIGHTS  AND  VOIDS   IN    NEW  YORK  SAND    WITH    VARIOUS 
PERCENTAGES  OF  200-MESH  DUST. 


Weight  per 
Cubic  Foot. 

Voids. 

Original  sand,  compacted  hot  

106  0 

35  5 

12  .  4%  of  dust  

114  0 

31  0 

16  7"  "     "                           .                   i 

116  0 

29  1 

20  6'    "     "  . 

120  2 

26  6 

24  2  '    "     " 

127  0 

23  0 

30  4'    "     "  . 

130  0 

21  2 

36.0'    "     "  

132  5 

20  0 

41.7'    "     "  

133.1 

19  7 

50  0'    "     "  

114  6 

24  7 

THE  MINERAL  AGGREGATE. 


When  the  densest  of  these  sand  and  dust  mixtures  is  added  to 
a  gravel  with  voids  of  35.1  per  cent  in  amount  sufficient  to  fill  the 
voids  in  the  latter  they  are  further  reduced  to  about  12.1  per  cent, 
and  the  aggregate  weighs  144.8  pounds  per  cubic  foot  as  compared 
to  164.1  pounds  for  solid  quartz. 

WEIGHT  PER  CUBIC  FOOT  AND  VOIDS  IN  CRUSHED  FLINT, 
GRADED  LIKE  THE  AVERAGE  SAND  IN  SEVERAL  CITIES, 
COMPARED  WITH  THE  LOCAL  SANDS  OF  THESE  CITIES 
OF  THE  SAME  GRADING,  WITH  NO  200-MESH  MATERIAL, 
WITH  13  PER  CENT  OF  200-MESH  FLINT  AND  13  PER  CENT 
OF  200-MESH  DUST.  SPECIFIC  GRAVITY  OF  FLINT  =  2. 65. 


- 

Without  200- 
Mesh  Material. 

With  200  Flint. 

With  200  Dust. 

Wt.  per 
Cu.  Ft. 

Voids. 

Wt.  per 
Cu.  Ft. 

Voids. 

Wt.  per 
Cu.  Ft. 

Voids. 

New  York—  1898: 
Local 

109.6 
105.5 

109.1 
103.4 

111.9 
103.6 

104.5 
99.6 

110.4 
103.0 

113.3 
105.3 

111.1 
107.6 

110.6 
104.3 

106.1 
109.0 

109.6 
100.1 

107.8 
104.5 

34.1 
38.1 

34.6 
37.4 

31.7 
37.1 

36.0 
39.5 

32.5 
37.6 

30.9 
36.2 

31.6 
34.8 

32.6 
36.8 

36.5 
34.0 

33.9 
39.4 

35.2 
36.7 

115.6 
109.0 

113.9 
104.9 

116.1 
108.3 

110.9 
107.0 

115.0 
106.2 

118.6 
106.6 

117.1 
112.6 

115.6 
109.4 

114.5 
113.5 

115.9 
103.9 

111.3 
106.5 

30.5 
34.0 

32.3 
36.4 

29.1 
34.4 

32.1 
35.2 

29.9 
35.7 

27.6 
34.2 

28.2 
31.8 

29.6 
33.7 

31.4 
31.8 

30.1 
37.1 

33.1 
35.5 

118.9 
110.9 

120.4 
107.4 

122.2 
111.8 

115.7 
112.2 

122.4 
113.5 

124.5 
113.5 

123.5 
116.0 

121.0 
112.4 

119.0 
118.1 

120.5 
108.6 

119.4 
113.9 

26.5 
32.9 

27.9 
34.9 

25.4 
32.3 

29.1 
32.0 

25.3 
31.0 

24.0 
31.2 

24.1 
29.7 

26.3 
31.9 

28.1 
26.5 

27.3 
34.2 

28.2 
31.0 

Flint 

Chicago  —  1898  : 
Local                     .    ... 

Flint                  

St.  Louis—  1899: 
Local  

Flint 

Louisville  —  1899  : 
Local 

Flint                        

Kansas  City—  1898: 
Local  

Flint 

Omaha—  1899: 
Local 

Flint                    

Trenton—  1898: 
Local  

Flint 

Paterson—  1899: 
Local 

Flint 

Washington—  1899  : 
Local  

Flint 

Buffalo—  1899: 
Local.  .            

Flint  

Philadelphia—  1899: 
Local 

Flint  . 

84 


THE  MODERN  ASPHALT  PAVEMENT. 


Sharp  as  Compared  with  Rounded  Sand. — If  particles  of  the 
crushed  quartz  of  sizes  corresponding  to  those  found  in  natural 
sand  are  combined  in  the  proportions  found  in  the  latter,  and  the 
voids  in  each  determined,  the  results  are  a  striking  illustration 
of  the  difference  in  the  degree  to  which  compaction  can  be  carried 
with  sand  made  up  of  sharp  and  rounded  particles.  (See  preceding 
table,  page  83) 

As  in  the  case  of  the  single-sized  particles  the  sharp  sands  do  not 
compact  as  well  as  those  with  rounded  particles,  and  as  the  greatest 
possible  compaction  is  desirable,  it  seems  that  a  rounded  sand  is 
more  suitable  for  the  construction  of  asphalt  pavements  than  a 
sharp  one.  Experience  has  shown  that  this  is  the  case.  The 
particles  should,  however,  be  rounded  and  not  round,  as  in  the 
latter  case  they  would  move  too  easily  on  one  another  and  give 
the  pavement  a  tendency  to  displacement  under  traffic.  It  will 
not  do,  however,  to  draw  too  general  conclusions  from  a  determina- 
tion of  voids  in  a  sand  alone.  Small  voids  are  desirable,  but  may 
at  the  same  tune  occur  in  sands  which  are  unsuitable  for  use  in  a 
surface  mixture.  For  example,  sands  too  coarse  to  permit  of 
being  employed  may  have  a  smaller  volume  of  voids  than  a  finer 
or  more  suitable  sand. 


Passing  Mesh. 

Total. 

Wt  per 
Cu.  Ft. 

Voids. 

200 

100 

80 

50 

25 
30 

40 

30 

20 

10 

Trenton 

0 
0 

11 
22 

14 

18 

14 
14 

12 

7 

13 

5 

11 

4 

=  100% 
=  100% 

111.1 
107.8 

31.6 
35.2 

Philadelphia. 

Here  the  coarse  sand  has  the  smaller  volume  of  voids,  which  is 
quite  often  the  case,  but  the  size  of  the  voids  is  too  large  and  the 
sand  is  consequently  undesirable.  It  is  therefore  necessary  to 
consider  the  grading  of  a  sand  as  well  as  its  voids  in  judging  it. 

Grading  of  Sands. — The  proper  grading  for  an  asphalt  mix- 
ture is  seldom  found  in  a  single  sand,  but  it  can  be  arranged  by 
mixing  two  or  more  containing  particles  of  different  sizes.  The 
character  of  the  sands  which  have  been  used  in  mixtures  in  various 
cities  is  illustrated  by  the  following  examples. 


THE  MINERAL  AGGREGATE. 
SAND  GRADING— VARIOUS  CITIES. 


85 


Cities. 

Passing  Mesh. 

Total. 

200 

100 

80 

50 

40 

30 

20 

10 

Chicago  —  fine,  1896  

10 
2 
2 
32 
0 
2 
2 
2 
6 
0 
14 
2 
17 
31 
2 
1 

68 
15 
1 
33 
1 
25 
19 
14 
13 
1 
26 
4 
40 
39 
9 
6 

15 
17 
4 
13 
2 
29 
19 
26 
14 
1 
14 
22 
30 
21 
36 
10 

5 
52 
53 
18 
36 
36 
41 
49 
31 
48 
38 
28 
10 
8 
49 
41 

2 
9 
25 
3 
32 
4 
12 
6 
20 
46 
6 
19 
1 
1 
3 
19 

2' 
10 
1 
17 
3 
3 
2 
10 
3 
2 
10 
1 

i 

15 

2 
3 

9 
1 
2 
1 
4 
1 

l6' 
1 

i 

2 
3 
2 

2 
0 

5 

=  100% 
=  100% 

=100% 

=  100% 
=  100% 
=  100% 
=  100% 
=  100% 

=  100% 
=  100% 
=  100% 
=  100% 
=  100% 
=  100% 
=  100% 

'  '       —  medium 

Louisville  —  river 

«  <        —  bar.                  

Milwaukee  —  coarse  beach  

<  <        —  White  Fish  Bay  

Omaha  —  single  sand,  1899  

Shelby  —  single  sand  1899 

Boston  —  single  sand,  1899 

St  Louis  —  coarse,  1897        .  .    . 

<       —  fine,  1897  

'       —  river,  coarse  .*.... 

__   «      foe  

Buffalo  —  bank  fine 

'       —  lake  fine 

'       —  "    coarse   . 

5 

3 

The  preceding  data  show  the  very  great  variations  in  the  charac- 
ter of  different  sands,  not  only  as  to  the  size  and  shape  of  the 
grains,  which  are  of  the  utmost  importance  in  preparing  a  surface 
mixture,  but  also  in  the  character  of  the  surface  of  the  grains.  It 
does  not  seem  too  much  to  say,  therefore,  that  the  selection  of  a 
suitable  sand  or  the  combination  of  two  or  more  in  a  proper  way  is 
as  important  a  detail  in  producing  a  satisfactory  asphalt  pavement 
as  the  regulating  of  any  of  the  other  constituents.  The  difficulties 
to  be  met  with  are  numerous  and  demand  experience  in  meeting 
them. 

Stone. — Stone  is  sometimes  used  as  a  part  of  the  mineral 
aggregate,  and  this  use  has  grown  of  late  years.  When  it  forms  the 
chief  portion  of  the  wearing  surface  the  latter  is  known  as  an 
asphaltic  concrete.  This  material  will  be  considered  in  a  later 
part  of  this  volume.1 

SUMMARY. 

In  this  chapter  the  very  varied  character  of  the  sand  which  is 
the  chief  constituent  of  the  mineral  aggregate  of  an  asphalt  surface 

1  Page  375. 


86  THE  MODERN  ASPHALT  PAVEMENT. 

mixture  has  been  shown,  and  that  skill  is  necessary  in  selecting  this 
material  for  the  preparation  of  a  satisfactory  mixture.  Sands  differ 
according  to  their  origin  and  the  source  from  which  they  are 
obtained.  They  differ  as  regards  the  size  of  the  grains  of  which 
they  are  made  up,  the  relative  proportion  of  different  sized  grains 
which  are  present,  the  shape  of  the  grains,  the  character  of  the 
surface  and  of  the  material  of  which  they  are  composed,  and 
the  proportion  of  the  voids  or  vacant  spaces  between  the  grains 
when  compacted.  They  also  vary  in  their  volume  weight,  a 
matter  of  importance  where  materials  are  mixed  by  weight  and 
not  by  volume. 

Altogether  there  seems  to  be  nothing  more  important  for  the 
construction  of  a  satisfactory  asphalt  surface  mixture  than  a 
thorough  understanding  of  the  peculiarities  of  the  various  sands 
and  of  their  adaptability  to  the  purpose  for  which  they  are  used. 


CHAPTER  IV. 
FILLER,  OR  DUST. 

A  FILLER,  or  dust,  is  made  a  part  of  the  mineral  aggregate  of 
asphalt  surfaces  for  the  purpose  of  rendering  the  surface  more 
dense,  so  that  it  will  be  less  acted  upon  by  water,  and  less  liable  to 
interior  displacement  or  movement.  Its  presence  in  a  surface 
mixture  may  be  looked  at  in  much  the  same  way  as  that  of  the 
finer  clay  particles  in  a  soil.  In  fact  soil  physics,  as  treated  by 
the  agricultural  physicists,  is  in  many  directions  instructive  as 
applied  to  surface  mixtures,  which  are  aggregates  of  small  particles 
like  soils  and  contain  more  or  less  bitumen  as  the  soils  do  more  or 
less  water. 

In  regard  to  the  different  parts  played  by  fine  and  coarse 
particles  in  a  soil,  Whitney  remarks :  l 

"In  a  symmetrical  arrangement  of  the  grains  in  a  soil  con- 
taining 47.64  per  cent 2  by  volume  of  empty  space,  each  grain  will 
touch  the  surface  of  six  adjacent  grains.  There  is  a  certain 
amount  of  surface  attraction  between  these  particles. 

"  If  the  grains  are  large  they  still  only  touch  at  six  points,  and 
the  weight  of  the  grains  is  sufficient  to  overcome  this  slight  sur- 
face attraction.  A  lump  of  wet  sand  will  fall  apart  as  it  dries, 
for  it  is  bound  together  by  the  contracting  power  of  the  film  of 
water  which  surrounds  it,  and  when  this  is  removed  by  evapora- 
tion the  weight  of  the  grains  is  sufficient  to  overcome  the  surface 
attraction  of  the  relatively  large  and  heavy  particles  and  they 
fall  apart. 

1  Bulletin  No.  4,  U.  S.  Weather  Bureau,  1892,  27. 

•Whitney  is,  of  course,  wrong  in  assuming  this  volume;  the  voids,  a-* 
has  been  shown  on  page  74,  might  be  25.95  per  cent. 

87 


88  THE  MODERN  ASPHALT  PAVEMENT. 

"If  the  grains  are  very  small,  like  grains  of  clay,  the  surface 
attraction  of  the  grains  is  sufficient  to  bind  the  mass  into  a  com- 
pact lump  when  dry;  for  while  there  are  still  only  six  points  of 
contact  for  any  one  grain,  there  are  many  other  grains  and  so  many 
more  points  of  contact  in  a  given  weight  of  material.  If  the  size 
of  the  grains  was  still  further  reduced  to  molecular  proportions 
the  mass  would  assume  the  hardness  and  rigidity  of  a  single  grain 
of  sand  or  clay." 

These  facts  apply  as  well  to  asphalt-surface  mixtures  as  to 
soils,  and  explain  the  parts  which  a  filler  plays. 

This,  however,  has  been  little  understood  heretofore  in  the 
paving  industry. 

Dust  in  the  Earlier  Days. — In  the  earlier  days  of  the  industry, 
and  even  as  late  as  1885,  the  Washington  specifications  for  asphalt 
pavements  read  that  the  mixture  shall  contain  12  to  15  per  cent 
of  carbonate  of  lime  and  that  "the  powdered  carbonate  of  lime 
will  be  of  such  a  degree  of  fineness  that  16  per  cent  by  weight 
of  the  entire  mixture  for  the  pavement  shall  be  an  impalpable 
powder  of  limestone  and  the  whole  of  it  shall  pass  a  No.  26  screen. 
The  sand  will  be  of  such  size  that  none  of  it  will  pass  a  No.  80 
screen  and  the  whole  shall  pass  a  No.  20  screen."  As  a  matter 
of  fact,  very  little  real  dust,  200  mesh,  was  put  in  the  mixture 
and  it  was  a  question  even  as  late  as  1893  whether  dust  con- 
tributed in  any  way  to  improve  it. 

That  it  is  of  the  greatest  value,  especially  in  surface  exposed 
to  heavy  traffic,  is  now  known.  The  difference  in  the  penetra- 
tion, ductility,  and  resistance  to  stress  of  the  same  bitumen  with 
and  without  filler  can  be  readily  shown.1  Filler,  therefore,  enables 
us  to  use  a  softer  cement  than  otherwise  would  be  the  case  and 
thus  make  an  asphalt  surface  less  liable  to  mark  in  hot,  less  brittle 
in  cold  weather,  and  far  less  liable  to  internal  displacement.  In 
the  earlier  asphalt  pavements  where  Trinidad  asphalt  was  the 
only  cementing  material  in  use  this  contained  in  itself  so  much 
fine  inorganic  matter  which  was  a  natural  filler  that  it  was  a  great 
help  to  the  surface  before  the  necessity  for  the  presence  of  a  high 
percentage  of  dust  was  understood. 

1  See  page  373 


FILLER,  OR  DUST.  89 

The  use  of  a  filler  is  well  illustrated  in  the  laying  of  coal-tar 
walks  in  England,  where  very  soft  coal-tar  is  mixed  with  all  the 
slaked  lime  it  will  hold,  often  more  than  50  per  cent  by  weight, 
and  this  mixture  used  as  a  cement  with  sand.  The  filler  makes 
it  possible  to  use  a  tar  so  soft  that  it  will  not  crack  in  winter,  while 
preventing  its  marking  excessively  in  summer. 

Varieties  of  Filler. — Numerous  kinds  of  mineral  matter,  ground 
to  a  more  or  less  fine  powder,  have  been  used  from  time  ta  time 
in  asphalt  mixtures  as  a  filler.  These  include 

Limestone,  Natural  hydraulic  cement, 

Hydraulic  limestone,  Portland  hydraulic  cement, 

Trap  rock,  Clay, 

Volcanic,  Ground  shale, 

Marl,  Dust-collector  dust, 

Silica,  Ground  waste,  lime   from  beet- 

Caustic  or  slaked  lime,  sugar  factories. 

Ground  Limestone  has  been  used  far  more  than  any  other  and 
was  the  original  material  employed  by  De  Smedt.  There  is  prob- 
ably nothing  better  than  this,  unless  it  be  Portland  cement,  for 
heavy-traffic  streets.  It  is  a  desirable  material,  as  asphalt  cement 
adheres  to  it  firmly  and  does  so  by  being  absorbed  by  it  to  a  cer- 
tain extent. 

Ground  hydraulic  limestone  has  also  been  used  where  it  could 
be  conveniently  and  cheaply  obtained  from  the  cement  manu- 
facturers. It  is,  no  doubt,  as  suitable  for  its  purpose  as  the  simple 
carbonate. 

Ground  Shale. — In  the  manufacture  of  shale  bricks  the  shale  is 
first  ground  to  a  powder  which  is  often  extremely  fine  and  in  con- 
sequence suitable  for  use  as  a  filler.  Such  a  shale  dust  is  available 
in  the  State  of  Washington,  91  per  cent  passing  a  200-mesh  screen 
and  79  per  cent  remaining  suspended  in  water  for  fifteen  seconds. 
Ground  Clay  or  loam  free  from  organic  matter  could  also  be 
used  in  a  similar  way.  A  large  part  of  the  natural  filler  in  Trinidad 
asphalt  is  clay,  and  on  this  account  it  was  thought  that  clay  might 
eventually  prove  the  most  desirable  filler,  as  owing  to  its  peculiar 
surface  and  porosity  it  will  absorb  bitumen  much  more  satisfac- 
torily than  any  of  the  ground  rock  fillers,  but  it  has  been  found  to 
have  such  a  small  volume  weight  and  to  be  so  light  and  fluffy  that 


90  THE  MODERN  ASPHALT  PAVEMENT. 

a  large  part  of  the  clay  is  blown  away  in  an  open  mixer  and  it  can 
only  be  used  successfully  in  a  tightly-closed  one,  which  is  rarely 
available.  In  this  connection  the  studies  of  Dr.  A.  S.  Cushman, 
of  the  Office  of  Public  Roads,  U.  S.  Department  of  Agriculture, 
on  'The  Nature  of  Clay"  and  on  "The  Adsorption  of  Solids  by 
Rock  Powders"  are  of  great  interest. 

Ground  Waste  Lime  from  Beet-sugar  Factories. — In  the  process 
of  defecating  the  diffusion  liquors  obtained  in  the  extraction  of 
sugar  from  beets  large  quantities  of  caustic  lime  in  the  form  of 
cream  of  lime  are  used,  which  is  subsequently  removed  from  the 
sugar  solution  by  nitration.  This  when  dried  and  ground  has  been 
suggested  for  use  as  a  filler  and  employed  to  a  small  extent  in 
California  and  Michigan.  As  far  as  fineness  is  concerned  it  is  a 
satisfactory  material,  but  it  contains  many  impurities  such  as 
organic  matter  in  the  form  of  sugar  and  organic  acids  combined 
with  lime.  Analysis  shows  that  it  has  the  following  composition: 

COMPOSITION   OF   DRIED   AND    POWDERED    BEET-SUGAR 
FILTER-PRESS  CAKE. 

Calcium  carbonate 78 .0% 

Free  lime 1.0 

Lime  combined  with  organic  matter 5.0 

Magnesia  carbonate 2.0 

Alkalies 2 

Iron  and  alumina 2.6 

Sulphuric,  phosphoric,  and  oxalic  acids 2.4 

Sugar 5.0 

Organic  not  sugar 2.1 

98.3 

It  is  to  a  certain  extent  an  open  question  whether  the  organic 
matter  will  prove  deleterious  to  the  surface  mixture  and  the  free 
lime  likewise.  Experience  alone  can  prove  the  availability  of 
this  material  as  a  filler. 

Ground  Marl  has  served  of  late  years  as  a  filler  in  those  cities 
near  the  marl-beds  of  Ohio  and  Michigan.  It  gave  fairly  satis- 
factory results,  but  its  disadvantage  lies  in  its  low  volume  weight, 
in  consequence  of  which  it  is  readily  blown  away  on  mixing  it  with 
sand,  and  its  use  has  been  discontinued. 

Ground  Silica. — Ground  sand  and  trap-rock  have  been  largely 
used  in  the  work  in  New  York.  It  is  questionable  if  it  is  desirable 


FILLER,  OR  DUST.  ,  91 

as  a  substitute  for  limestone,  as  asphalt  does  not  adhere  to  it  as 
well  and  it  cannot  be  ground  as  fine.  It  is  a  filler,  however,  and 
successful  results  have  been  obtained  with  it. 

As  between  ground  limestone  and  silica  or  silicate  dusts,  experi- 
ments of  Mr.  F.  P.  Smith,  formerly  of  the  Alcatraz  Asphalt  Co., 
have  shown  that  the  former  enables  a  mixture  made  with  it  to 
resist  water  action  better  than  the  silica  filler,  and  this  can  be 
readily  understood  for  the  reason  that  has  been  given,  namely, 
that  bitumen  will  adhere  to  the  former  much  more  firmly  than  to 
the  latter  by  being  partly  absorbed  by  it. 

Caustic  and  Slaked  Lime. — These  fillers  have  only  been  used 
experimentally.  They  are  largely  employed  in  coal-tar  work. 
No  peculiarities  have  been  noticed  in  the  small  amount  of  work 
done  with  them,  but  in  the  laboratory  cylinders  of  surface  mixture 
containing  caustic  lime  expanded  badly  on  immersion  in  water. 
It  would  probably  not  be  desirable  to  experiment  further  with 
their  use. 

Natural  Hydraulic  Cement. — This  material  began  to  be  used 
as  a  filler  in  cases  where  limestone  dust  was  not  available.  How- 
ever, of  late  years  its  use  has  been  abandoned,  as  it  has  been  observed 
that  surfaces  laid  with  this  material  as  a  filler  have  cracked  more 
than  where  limestone  was  the  ground  material.  It  seems  to 
possess  the  property,  perhaps  owing  to  the  presence  of  free  lime, 
of  hardening  the  asphalt  cement  very  rapidly.  If  it  is  necessary  to 
use  such  a  filler  the  cement  should  be  at  least  20  points  softer  than 
would  be  the  case  with  other  materials. 

Portland  Cement. — This  is  a  material  which,  for  some  reason 
not  yet  satisfactorily  explained,  gives  the  best  results  as  a  filler  in 
asphalt  surfaces,  especially  on  streets  of  heavy  traffic  or  where 
the  surface  is  subject  to  the  action  of  water.  Its  desirability 
may  be  due  to  its  capacity  for  adsorbing  a  thick  film  of  bitu- 
men, but  it  cannot  with  certainty  be  attributed  to  its  hydraulic 
properties. 

A  cylinder  of  open  Trinidad  asphalt  surface  mixture,  made  up  in 
Washington,  D.  C.,  in  1894,  half  of  which  contained  limestone 
dust  as  a  filler  and  the  other  Portland  cement,  showed  the  most 
striking  contrast  in  its  appearance  after  nearly  six  years'  immersion 


92  THE  MODERN  ASPHALT  PAVEMENT. 

in  water,  the  portion  containing  Portland  cement  being  still  hard 
and  firm,  while  the  ordinary  limestone  mixture  was  much  more 
strongly  acted  upon. 

The  slight  extra  cost  of  Portland  cement  is  more  than  made 
up  by  the  improvement  in  the  character  of  the  surface,  where 
especially  trying  conditions  are  to  be  met,  and  its  use  is  highly  to 
be  commended. 

Fine  Grinding  of  the  Filler. — The  material  which  is  of  value  in  a 
filler  is  the  impalpable  dust,  much  finer  than  the  particles  merely 
passing  a  200-mesh  sieve.  Sandy  particles  of  dust  of  about  the 
200-mesh  size  are  probably  of  somewhat  greater  value  than  the 
200-mesh  rounded  particles  of  an  ordinary  sand,  which  are  at 
times  distinctly  disadvantageous  in  a  mixture,  as  they  are 
sharper.  Larger  particles  do  not  differ  from  sand  grains  of  the 
same  size. 

It  is  important,  therefore,  in  securing  a  filler  that  it  should 
contain  as  much  real  dust  as  possible.  If  there  is  only  45  per 
cent  of  this  material,  twice  as  much  must  be  used  as  if  it  contained 
90  per  cent.  In  the  former  case  the  sand  must  be  heated  to  a 
much  higher  temperature  to  take  care  of  so  much  cold  material, 
while  in  the  other,  as  a  matter  of  economy,  the  smaller  bulk  to  be 
handled  to  accomplish  the  same  object  is  an  important  con- 
sideration. 

As  it  is  difficult  to  find  a  desirable  filler  on  the  market,  dust 
should  be  ground  by  paving  companies  themselves.  It  can  be 
turned  out  with  a  tube-mill  85  to  95  per  cent  fine.  There  is  no 
question  but  that  the  production  and  use  of  such  dust  will  pay 
if  for  no  other  reason  than  to  do  away  with  the  excessive  cooling 
of  the  mixture  caused  by  the  addition  of  the  large  quantities  of 
cold,  coarse  material  to  the  sand  which  are  necessary  to  obtain 
a  sufficient  amount  of  true  filler. 

More  Refined  Methods  of  Examining  Filler. — Up  to  the  present 
point  fillers  have  chiefly  been  spoken  of,  as  to  their  fineness,  accord- 
ing to  the  amount  which  will  pass  a  200-mesh  sieve,  the  finest 
wire  sieve  that  is  made.  As  has  been  said,  the  material  passing 
this  sieve  may  be  much  of  it  sand  smaller  than  .10  mm.  in  diam- 
eter, and  very  little  of  it  may  be  true  dust  or  filler  of  a  diameter 


FILLER,  OR  DUST.  93 

smaller  than  .025.  The  difference  in  character  of  the  two  sizes 
is  readily  seen  on  inspection. 

In  judging  the  value  of  a  filler  it  is  desirable  to  determine  the  rela- 
tive amount  of  these  materials,  coarse  material,  and  the  impalpable 
dust.  As  there  are  no  finer  sieves  than  the  200-mesh,  this  can  only 
be  done  by  elutriation,  or  washing  with  water,  the  coarser  grains 
settling  out  rapidly  and  the  finer  more  slowly.  The  manner  of 
doing  this  is  as  follows: 

Five  grams  of  the  dust  to  be  examined  are  placed  in  a  beaker 
about  120  mm.  high,  holding  about  600  c.c.  The  beaker  is  nearly 
filled  with  distilled  water,  at  a  temperature  of  exactly  68°  F., 
and  agitated  with  an  air-blast  until  the  dust  and  water  are  thor- 
oughly mixed,  taking  care  not  to  produce  cyclonic  currents  hi 
the  latter.  On  stopping  the  blast  the  liquid  is  allowed  to  stand 
exactly  15  seconds  and  the  water  above  the  sediment  immediately 
decanted  without  pouring  off  any  of  the  latter.  ^This  washing 
is  repeated  three  times.  The  sediment  is  then  washed  out  into 
a  dish,  dried,  and  weighed.  The  loss  hi  weight  represents  that 
portion  which  may  be  considered  as  dust  free  from  sand.  The 
washing  must  be  done  with  distilled  water  and  at  a  definite  tem- 
perature. 

This  method  can  also  be  used  with  hydraulic  cements  or  mate- 
rials acted  upon  by  water,  since  the  finer  portion  is  the  only  part 
acted  upon,  while  the  coarser  part,  which  is  recovered  and  weighed, 
is  not  acted  upon  at  all. 

The  differentiation  of  the  particles  not  subsiding  in  15  seconds 
can  be  carried  further,  if  desired,  by  reagitating  the  decanted 
liquid  and  allowing  the  sedimentation  to  go  on  for  1  minute,  30 
minutes,  1  hour,  and  so  on.  For  ordinary  purposes  this  is  unneces- 
sary.1 The  size  of  the  particles  obtained  by  elutriation  can  be 
measured  in  the  same  way  as  that  of  the  particles  passed  by 
the  finer  sieves,  as  described  by  Hazen.  The  size  of  these 
particles  among  ordinary  fillers  will  be  found  in  the  following 
table: 


1  For  further  details,  see  Hazen,  24th  Annual  Report  Massachusetts  State 
Board  of  Health,  1892,  541. 


94 


THE  MODERN  ASPHALT  PAVEMENT. 


VOLUME  WEIGHT  OF  DUST. 


Test  number  

75803 

75804 

75805 

75806 

71076 

75791 

Dust  

Lime- 

Trap 

Port 

Clav 

Marl 

Vol- 

stone 

rock 

cement 

canic 

84  0% 

81% 

74% 

93% 

92% 

100% 

"       100-    "    

14.0 

18 

19 

5 

4 

80-    "    

2.0 

1 

6 

1 

2 

"         50-    "   

1 

1 

2 

Elutriation   test  not  set- 

tled in  15  seconds  

71.3% 

70.3% 

56.7% 

87.8% 

80.3% 

98.2% 

Pounds  per  cubic  foot.  .  .  . 

113.7 

112.3 

123.5 

78.0 

78.0 

63.4 

A  number  of  dusts  from  various  parts  of  the  country  have  been 
differentiated  and  the  results  are  as  follows: 

SIZE  OF  PARTICLES  IN  VARIOUS  FILLERS. 


Test  No. 

Character. 

Per  Cent 
Passing 
200. 

Per  Cent 
on  200. 

30915 

Limestone. 

96 

4 

30963 

Silica. 

96 

4 

30267 

Limestone. 

91 

9 

30578 

«  « 

93 

7 

30715 

« 

48 

52 

30716 

<  « 

66 

34 

30766 

Silica. 

67 

33 

30606 

Marl. 

91 

9 

In  these  fillers,  as  supplied  for  use,  there  was  present 
the  percentages  of  particles  passing  a  200-mesh  sieve  shown  in 
the  preceding  table. 

This  200-mesh  material  consists  of  the  following  sized  par- 
ticles: 


FILLER,  OR  DUST. 


95 


Average 

Test  No. 

Time  of 

Size  of 

Less  than 

30015 

30963 

30276 

30578 

30715 

30716 

30766 

30606 

Difference  and 

loss 

001     mm. 

4  4 

1   0 

3  8 

4 

2  7 

11  9 

3  2 

2.4 

16  hours  

.0025       ' 

2.8 

4.2 

2     "    

.0075      ' 

5.0 

2.9 

4.9 

5.4 

3.1 

3.2 

3.0 

7.7 

30  minutes.  .  . 

.025 

51.3 

42.4 

55.1 

67.4 

32.5 

23.9 

23.3 

66.5 

1  minute  

.050 

17.7 

9.3 

15.0 

12.9 

24.8 

20.1 

25.6 

13.0 

15  seconds.  .  .  . 

.080 

18.8 

40.2 

21.2 

13.9 

36.9 

40.9 

44.9 

10.4 

100.0 

100.0 

100.0 

100.0 

100.0 

100.0 

100.0 

100.0 

Actual  dust  in 

original  ma- 
terial small- 

er than  

.050      " 

78.0 

55.6 

71.7 

80.1 

30.3 

39.0 

36.9 

80.5 

As  showing  the  variation  in  the  amount  of  material  which 
is  not  ground  even  fine  enough  to  pass  a  200-mesh  sieve  the  first 
data  given  may  be  examined.  The  coarse  material  varies  from 
4  per  cent  in  high-grade  fillers  to  52  per  cent  in  an  inferior  article. 
Separating  out  and  rejecting  this  coarse  material  as  of  no  value 
greater  than  that  of  sand  the  finer  grams  were  separated  by  elu- 
triation  into  the  particles  of  the  sizes  given. 

It  seems  fair  to  consider  that  particles  smaller  than  .050  mm. 
in  average  diameter  are  the  only  portions  of  a  filler  to  be  con- 
sidered as  true  dust,  and  it  will  be  seen  that  of  the  entire  mate- 
rial in  several  instances  only  30-40  per  cent  is  dust  and  the  remain- 
der sand. 

A  good  filler  should  contain  at  least  60  per  cent  of  its  weight 
of  actual  dust  and  preferably  over  70  per  cent. 

An  examination  of  a  filler  or  even  a  mixture  in  this  way  is 
very  serviceable  in  revealing  the  actual  amount  of  fine  dust  which 
either  may  conHH.  In  a  mixture  examined  in  New  York  the 
actual  amount  of  dust  of  different  sizes  is  shown  in  the  following 
analysis: 


96  THE  MODERN  ASPHALT  PAVEMENT. 

TEST  NO.  30954. 
Bitumen 11 .0% 


Settling  in, 
Time. 

Size  of 
Particles 
Less  than 

Passing  200.  .. 

Difference, 

or  loss.  . 

8%.... 

« 

(1 

2  hours.  .  . 

.0075mm. 

.3 

« 

tt 

30  minutes. 

.025     " 

2.5 

tt 

1  1 

1  minute.. 

.050     " 

4.2 

ft 

tt 

15  seconds. 

.080     " 

10.2 



18.0 

« 

100.  .. 

14  0 

tt 

80.  .. 

15  0 

tt 

50.  . 

25  0 

tt 

40.  .. 

10  0 

tt 

30.  .. 

2.0 

It 

20.  . 

3  0 

tt 

10.. 

2.0 

200  Mesh 

on  100 

Per  Cent 

Basis. 

4-2% 

1.6 
13.8 
23.8 
56.6 

100.0 


100.0 

Sand 77.6% 

Dust 5.4 

Trinidad  A.  C 17.0 

100.0 

The  dust  was  the  finest-ground  limestone  of  the  composition 
given  in  the  preceding  table.  It  contained,  as  used,  81.2  per 
cent  of  particles  not  subsiding  in  15  seconds.  From  the  amount 
of  dust  in  use  it  is  readily  calculated  that  no  more  than  4.3  per 
cent  of  material  which  acts  as  a  filler  would  be  expected  in  the 
mixture.  7.9  per  cent  is  actually  found,  the  excess  over  the  cal- 
culated 4.3  per  cent  being  due  to  the  fine  material  derived  from 
that  in  the  Trinidad  asphalt.  The  small  percentage  of  real  dust 
in  some  of  our  mixtures  is  therefore  striking. 

SUMMARY. 

The  character  of  the  filler  or  finely  ground  inorganic  matter 
which  enters  into  the  composition  of  the  mineral  aggregate  of 
an  asphalt  surface  has  been  shown  in  the  preceding  chapter  to 
be  a  matter  of  very  considerable  importance.  Impalpably  fine 
mineral  matter  of  various  kinds  can  be  satisfactorily  used,  but 
it  should  be  as  fine  as  possible,  and  for  construction  of  an  asphalt 


FILLER,  OR  DUST.  97 

pavement  on  streets  of  heavy  travel  Portland  cement  should  alone 
be  used  as  a  source  of  supply. 

The  intelligent  use  of  filler  in  an  asphalt  surface  mixture  demands 
further  careful  consideration  from  a  physical  point  of  view,  and 
the  investigations  which  have  been  carried  on  in  regard  to  rock 
powders  in  the  Office  of  Public  Roads,  U.  S.  Department  of 
Agriculture,  have  thrown  much  light  upon  this  subject. 


CHAPTER  V, 

THE   NATURE   OF   THE   HYDROCARBONS   WHICH   CONSTITUTE 
THE   NATIVE   BITUMENS. 

ASPHALT  cement  is  the  distinctive  feature  of  an  asphalt  pave- 
ment. It  serves  to  bind  the  mineral  aggregate  together  and 
enables  it  to  carry  traffic  without  displacement. 

It  consists  of  some  native  asphalt  or  other  hard  native  bitu- 
men, fluxed  with  some  soft  bitumen  in  the  form  of  dense  petro- 
leum oil  or  maltha,  or  of  some  hard  residue  from  the  distillation 
or  treatment  of  asphaltic  petroleum,  softened  to  a  proper  con- 
sistency in  the  same  way. 

Asphalt  cement  is,  therefore,  native  bitumen  and  its  intelli- 
gent consideration  necessitates  a  knowledge  of  and  the  differentia- 
tion of  the  various  native  bitumens  of  which  it  may  be  made  up. 

The  hydrocarbons,  or  compounds  of  hydrogen  and  carbon, 
which  when  mixed  in  varying  proportions  constitute  the  sub- 
stances which  are  known  as  bitumen,  belong  to  different  series, 
so  called,  which  are  characterized  by  the  relative  proportion  of 
hydrogen  and  carbon  atoms  which  they  contain  and  by  their 
structure  or  the  relation  of  the  carbon  atoms  to  one  another  in 
space.  A  short  explanation  in  regard  to  the  structure  of  the 
various  hydrocarbons  of  these  series  is  necessary  for  an  intelli- 
gent understanding  of  their  properties  as  affecting  the  character 
of  the  bitumen  in  use  in  asphalt*  pavements. 

Chain  Hydrocarbons. — The  carbon  atom  is  characterized 
chemically  as  being  quadrivalent;  that  is  to  say,  it  possesses  four 
affinities,  bonds,  or  links  by  means  of  which  it  may  be  said  to 
combine  with  atoms  of  other  elements.  The  hydrogen  atom 
has  but  one  bond  and  is  univalent. 

98 


NATURE  OF  THE  HYDROCARBONS.  99 

If  a  carbon  atom  combines  with  all  the  hydrogen  atoms  that 
it  is  capable  of,  its  four  bonds  must  each  be  linked  with  a  hydrogen 
atom,  and  the  resulting  molecule  will  consist  of  one  atom  of  car- 
bon and  four  of  hydrogen,  which  can  be  represented  by  the  symbol 
CH4,  in  which  C  stands  for  one  carbon  atom  and  H4  for  four  hydro- 
gen atoms.  In  this  substance  or  compound,  which  is  known 
as  methane,  or  marsh-gas,  we  have  the  carbon  atom  saturated 
as  to  its  affinities,  or  bonds,  with  hydrogen  atoms.  It  cannot 
combine  with  any  other  atom  except  by  replacing  with  it  one 
or  more  of  the  hydrogen  atoms.  It  is,  therefore,  known  as  a 
saturated  hydrocarbon. 

If  two,  three,  or  more  atoms  of  carbon  are  combined  in  the 
same  way  to  form  a  molecule  having  €2  or  €3,  etc.,  in  its  com- 
position, these  carbon  atoms  are  themselves  linked  or  bonded 
together  by  one  or  more  of  the  bonds  of  each  atom,  so  that  we 
may  have: 

One  carbon  atom  with  its  four  affinities  or  bonds  which  may 
be  represented  thus: 


4- 


i 

Two  carbon  atoms  joined  by  one  affinity  of  each  thus? 


44- 


Or  by  two  affinities  of  each  thus: 


u 


In  the  case  of  two  carbon  atoms  joined  by  one  affinity  each, 
there  are  six  bonds  remaining  to  unite  with  hydrogen.  The  result- 
ing compound  with  hydrogen  in  this  case  is  represented  by  the 
symbol  or  formula  C2H6.  It  is  a  saturated  hydrocarbon  in  the 
same  way  that  CH4,  with  one  atom  of  carbon,  is,  because,  while 
two  bonds  out  of  the  eight  of  the  two  carbon  atoms  are  necessarily 


100  THE  MODERN  ASPHALT  PAVEMENT. 

joined  in  linking  the  carbon  atoms  together,  all  the  remaining 
available  affinities  are  satisfied  by  hydrogen.  In  the  same  way 
with  three  atoms  of  carbon  in  the  molecule  we  have  the  carbon 
atoms  linked  to  each  other,  so  that  eight  affinities  out  of 
twelve  remain  to  be  saturated  by  hydrogen  thus: 

H    H    H 
H— C— C— C— H 


One  atom  is,  of  course,  linked  to  two  others,  and  so  two  affini- 
ties of  this  atom  are  not  available  for  combining  with  hydrogen. 
This  saturated  hydrocarbon  is  represented  by  the  symbol  CsHg. 

As  the  carbon  atoms  increase  in  number  there  is  found  to  be 
a  regular  increase  in  those  of  hydrogen,  so  that  the  compounds  of 
this  saturated  nature  become  what  is  called  a  homologous  series, 
differing  by  one  carbon  and  two  hydrogen  atoms  from  the 
following  and  preceding. 

CH4,  C2Hg,  CaHg,  CnH.2n+2> 

If  in  any  of  these  simple  chain  hydrocarbons,  which  owing 
to  the  simplicity  of  their  constitution  are  known  as  normal  hydro- 
carbons, one  of  the  hydrogen  atoms  is  supposed  to  be  removed,  a 
group  is  left  with  one  free  affinity,  or  if  two  hydrogens  or  more 
are  removed,  with  two  or  more  affinities.  These  imaginary  groups 
of  atoms  with  different  affinities  are  known  as  radicals.  They 
can  combine  with  other  similar  radicals  or  with  other  elements, 
such  as  the  halogens,  or  with  acid  radicals.  Thus  we  may  have 


CH 

Saturated.        Methyl.  Methylene.       Methenyl. 

If  different  hydrocarbon  radicals  are  substituted  for  hydrogen 
in  other  hydrocarbons  new  hydrocarbons  result.  In  this  way 
hydrocarbons  are  produced  which  have  the  same  composition 
or  number  of  carbon  and  hydrogen  atoms  as  in  the  normal  hydro- 
carbon, but  a  different  structure.  For  pentane,  therefore,  C5H12 
there  may  be  three  forms: 


NATURE  OF  THE  HYDROCARBONS.  101 

CH3 — CH2 — CH2 — CH2 — CH3 
CH3— CH— CHa— €H3 
CH3 

CH3 
H3C— C— CH3 

CH3 

Here  the  straight  chain  is  converted  into  one  with  one  or  more 
radicals  known  as  side-chains. 

These  hydrocarbons  are  denominated  normal  pentane,  iso- 
pentane,  and  tetramethylmethane,  the  latter  being  methane  in 
which  the  four  hydrogen  atoms  are  substituted  by  methyl  groups. 
They  are  also  known  as  isomers,  since  they  contain  the  same  num- 
ber of  carbon  and  hydrogen  atoms;  that  is  to  say,  have  the  same 
percentage  composition  but  a  different  structure  and  different 
physical  properties. 

With  similar  hydrocarbons  in  which  the  carbon  atoms  are 
greater  hi  number  the  possible  variations  in  structural  arrange- 
ment are  much  more  numerous,  and  it  can  be  readily  seen  that 
the  number  of  different  paraffin e  hydrocarbons  is  enormous. 

These  compounds  of  carbon  and  hydrogen  illustrate  what 
is  meant  by  a  series  of  hydrocarbons,  which  is,  in  this  case,  a  satu- 
rated series  known  as  the  paraffine,  limit,  or  chain  series,  since 
the  carbon  atoms  are  represented  as  linked  in  the  form  of  a  chain. 
It  is  the  series  which  makes  up  the  greater  part  of  ordinary  Penn- 
sylvania and  Ohio  petroleum  and  the  residuum  made  from  these 
oils. 

In  this  series,  the  carbon  being  combined  with  as  much  hydro- 
gen as  possible,  there  is  the  largest  percentage  of  hydrogen  and 
the  smallest  percentage  of  carbon  found  in  any  hydrocarbons 
of  a  given  number  of  carbon  atoms.  For  marsh-gas,  CH4,  it 
is  75  per  cent  carbon  and  25  per  cent  hydrogen,  a  proportion 
gradually  diminishing  as  the  number  of  carbon  atoms  increases. 
For  example,  for  C30H62  it  is  carbon  85.31,  hydrogen  14.69. 


102  THE'  MODERN  ASPHALT  PAVEMENT. 

Unsaturated  Hydrocarbons.  —  When  fhe  carbon  atoms  in  a 
hydrocarbon  do  not  combine  with  all  the  hydrogen  atoms  they 
might,  the  remaining  affinities  are  satisfied  in  joining  the  carbon 
atoms  together,  in  addition  to  the  single  bond  found  in  the  satu- 
rated series.  The  linking  of  the  carbon  atoms  is  then  doubled 
and  the  hydrocarbons  may  be  represented  thus: 

H    H  H         H 

C=C  C=C—  C—  H 


Owing  to  the  double  bond,  two  affinities  which  in  the  unsatu- 
rated  series  were  combined  with  hydrogen,  are  now  linked  with 
each  other  and  a  new  series  is  determined  in  which  the  hydrogen 
atoms  number  always  twice  the  carbon  atoms.  The  affinities  of 
the  carbon  are  not  entirely  satisfied  with  hydrogen,  and  the  hydro- 
carbons are  known  as  unsaturated  hydrocarbons.  As  the  rela- 
tion of  carbon  to  hydrogen  is  constant  the  percentage  composition 
of  all  the  hydrocarbons  of  the  CnH2w  series  is  carbon  85.71,  hydro- 
gen 14.29,  the  amount  of  hydrogen  being  always  less  than  in  any 
of  the  hydrocarbons  of  the  saturated  series  containing  the  same 
number  of  carbon  atoms. 

In  this  series,  which  is  known  as  the  Olefine  Hydrocarbons, 
but  two  of  the  carbon  affinities  are  joined  by  a  double  bond.  More 
of  these  affinities  may  be  joined  in  this  way,  resulting  in  other 
series  represented  by  the  general  formula  CnH2n_2,  CnH2n-4, 
CnH2n-6,  etc.,  in  which  the  per  cent  of  hydrogen  is  still  less. 

The  hydrocarbons  of  these  series,  it  is  plain,  are  even  more 
unsaturated. 

Hydrocarbons  in  general  are  divided,  therefore,  into  those 
which  are  saturated  and  those  which  are  unsaturated,  the  former 
being  stable  and  the  latter  reactive  and  very  susceptible  to  change, 
combining  with  or  being  converted  into  other  hydrocarbons  by 
the  action  of  sulphuric  acid  and  other  reagents.  The  saturated 
can  be  separated  from  the  unsaturated  hydrocarbons  by  strong 
sulphuric  acid,  and  this  will  be  found  to  be  a  very  important  means 
of  differentiating  the  oils  and  the  solid  bitumens  among  them- 


- 
NATURE  OF  THE  HYDROCARBONS.  103 

selves,  by  determining  the  relative  proportions  of  these  two  classes 
of  hydrocarbons  which  they  contain. 

Cyclic  Hydrocarbons. — In  the  preceding  hydrocarbons  the 
carbon  atoms  have  been  imagined  as  being  linked  in  the  form 
of  a  chain  of  more  or  less  simplicity.  It  can  readily  be  imagined 
that  the  normal  chain  can  be  bent  into  the  form  of  a  circle  so 
that  the  carbon  atoms  at  the  ends  may  be  united  with  each  other 
by  one  of  each  of  their  three  affinities.  In  this  way  a  ring  is  formed, 
each  carbon  atom  of  which  has  only  two  affinities  unsaturated, 
but  which  possesses  no  double  bond  when  these  affinities  are  all 
satisfied  with  hydrogen,  so  that  although  its  general  formula  is 
CnH2n,  the  same  as  that  of  the  unsaturated  olefines,  they  are 
saturated  hydrocarbons. 

Owing  to  reasons  which  it  is  unnecessary  to  go  into  in  this 
place  the  carbon  atoms  in  such  a  ring  do  not  exceed  seven  hi  num- 
ber, as  above  that  they  would  be  quite  unstable  and  could  not 
exist.  The  most-  stable  rings  are  those  of  five  and  six  atoms,  and 
hydrocarbons  with  this  number  are  the  foundation  or  source  of 
many  of  the  solid  native  bitumens.  Their  structure  may  be 
represented  as  follows: 

CH2— CH-K  CH2— CH2-€H2 

>CH2  or  C5H10  |       or  C6H12 

CH2— CH2/  CH2— CH2— CH2 

Pentamethylene.  Hexamethylene. 

The  carbon-hydrogen  groups  of  which  they  are  made  up  are 
the  groups  or  radicals  known  as  methylene. 

For  this  reason  the  hydrocarbons  are  known  as  a  class  as  the 
polymethylenes,  pentamethylene  being  the  hydrocarbon  of  five 
groups,  hexamethylene  the  one  of  six.  The  generic  name  of 
naphthenes  is  also  applied  to  the  series,  having  been  used  to  desig- 
nate the  polymethylenes  occurring  in  Russian  petroleum  before 
their  structure  was  elucidated.  They  are  distinguished  by  the 
fact  that,  although  not  as  stable  as  the  paraffine  hydrocarbons, 
they  still  possess  the  stability  of  saturated  compounds  and  are 
unacted  upon  by  strong  sulphuric  acid. 

In  these  polymethylenes,  as  in  the  normal  chain  hydrocarbons, 
one  or  more  of  the  hydrogen  atoms  can  be  substituted  by  radicals 


104  THE  MODERN  ASPHALT  PAVEMENT. 

like  methyl.  We  have,  for  instance,  methylpentamethylene,  in 
which  one  of  the  hydrogen  atoms  of  one  of  the  methylene  groups 
in  pentamethylene  is  substituted  by  CH3  the  methyl  group: 


<j\ 

>CH—  CH3 
CH2-CH/ 

or 


It  will  be  noted  that  this  hydrocarbon  has  the  same  formula 
as  hexamethylene  and  differs  from  it  only  in  structure.  They 
are  isomers. 

More  complicated  chains  can  exist,  as  where  the  radical  propyl 
CaHr  or  others  replace  the  methyl  radical  and  the  possibilities  in 
number  and  isomerism  is  again  immense. 

The  more  complicated  single-ring  polymethylenes  with  side- 
chains  are  more  reactive  than  the  simple  naphthenes. 

Unsaturated  Cyclic  Hydrocarbons.  —  Corresponding  to  these 
so-called  cyclic  saturated  hydrocarbons,  hi  which  the  carbon 
atoms  are  only  united  with  each  other  by  one  bond,  unsaturated 
cyclic  hydrocarbons  exist  in  which  double  bonds  occur.  The 
most  familiar  hydrocarbon  of  this  type  is  benzol,  derived  from 
coal-tar,  which  has  the  folio  whig  structure: 

H 


,4 


/NC-H 

II       ' 

C— H 

/ 

C 


This  forms  a  new  series  known  as  the  benzol  or  aromatic  series, 
the  general  formula  for  which  is  CnH2n-6- 

These  hydrocarbons  occur  in  a  greater  or  less  degree  in  all 
petroleums,  at  least  among  the  more  volatile  portions,  and  are 
particularly  prominent  in  California  and  Russian  petroleum. 


NATURE  OF  THE  HYDROCARBONS.  105 

Where  the  number  of  double  bonds  is  fewer  than  in  the  benzol 
ring  other  series  of  hydrocarbons  are  formed,  known  as  the  hydro- 
aromatic  series,  the  hydrocarbons  of  which,  in  then*  constitution, 
are  between  the  saturated  polymethylenes  and  the  aromatic  com- 
pounds. The  terpenes  are  members  of  this  series,  but  they  are 
not  found  hi  the  solid  native  bitumens  used  in  pavements.  Hexa- 
hydrobenzol  is  the  same  thing  as  hexamethylene  and  is  a  saturated 
hydrocarbon.  Tetrahydrobenzol  is  an  unsaturated  hydrocarbon 
corresponding  in  the  cyclic  series  to  the  olefines  of  the  chain  hydro- 
carbons. 

In  all  of  these  aromatic  and  hydrated  aromatic  hydrocarbons, 
as  well  as  in  the  saturated  polymethylenes,  any  or  all  of  the  hydro- 
gen atoms  may  be  substituted  by  paramne  or  olefine  radicals, 
thus  making  it  possible  to  form  a  vast  number  of  new  hydro- 
carbons containing  side-chains,  of  which  toluol,  or  methyl  benzol, 
is  a  type  in  the  aromatic  series,  as  was  methyl  pentamethylene 
in  the  polymethylene  series. 


C — CH3          CH2 — CIi2\ 

II  I  \C-H-CHs 

H— C       C— H  CHjj— CH/ 

Methy  Ipen  tame  thy  lene . 


Methylbenaol. 

Dicyclic  Hydrocarbons. — The  cyclic  hydrocarbons  thus  far 
considered  have  consisted  of  but  one  ring.  Dicyclic  and  poly- 
cyclic  hydrocarbons  are  also  known  to  exist  in  which  two  or  more 
rings  may  be  united  by  having  carbon  atoms  in  common,  as  in 
the  case  of  naphthalene,  CioH8,  the  result  of  the  condensation 
of  two  benzol  rings: 


106  THE  MODERN  ASPHALT  PAVEMENT. 

H       H 


-H 


yy 


H 

or  of  three  rings,  as  in  anthracene; 
H       H       H 

i   i   A 

/\    /\    /\ 

H— C       C       C       C— H 

I         II        II        II  orC14H10 

,    H— C       C       C       C— H 

\/  v  V 

C        C        C 

I     I     I 

H       H       H 

The  latter  substance  may  also  be  considered  as  consisting  of 
two  benzol  rings  united  by  two  methenyl  radicals. 

The  benzol  rings  may  also  be  united  by  free  affinities  or  by 
one  or  more  methylene  radicals  without  common  carbon  atoms, 
as  in  diphenyl,  CoH.5 — CeHs,  as  dibenzyl,  CoH.5 — CH2 — CH2 — CeHs, 
stilbene,  C6H5CH=:CHC6H5,  or  as  tolane,  C6H5C=C  C6H5. 

These  hydrocarbons  are  mentioned,  not  from  their  immediate 
interest  in  connection  with  the  bitumens,  as  they  only  occur  in 
coal-tar,  but  as  showing  the  infinite  variation  in  structure,  which 
is  possible. 

Polycyclic  Polymethylenes. — In  the  polymethylene  series 
bicyclic  and  pqlycyclic  hydrocarbons  also  exist,  in  which  two  or 
more  rings  have  common  carbon  atoms,  but  instead  of  two  carbon 
atoms  being  common  to  both  rings,  as  in  naphthalene,  three  such 
are  found  in  the  bicyclic  polymethylenes,  forming  what  is  known 
as  a  bridge  structure.  This  is  illustrated  by  two  hydrocarbons 


NATURE  OF  THE  HYDROCARBONS.          107 

prepared  synthetically  by  Rabe  and  Weilinger1  and  having  the 
following  structure  : 


CH2— C  (CH3)— CH2        CH2— OH 

I  I  -CH3 

CH2  CH2          CH2  CH2    CH.CH3    CH.CH 

I  I  -CH3 

CH2-CH CH2  CH2-CH CH2 

Methyl-bicyclo-ndhane.  Isopropyl-methyl-bicyclo-nonane. 

The  latter  hydrocarbon  has  probably  been  found  by  Coates 
in  Louisiana  and  by  Mabery  in  Santa  Barbara,  Cal.,  petroleum,2 
as  can  be  seen  from  the  close  correspondence  in  the  physical  and 
other  characteristics  of  the  synthetic  and  native  hydrocarbons. 

Synthetic.  Louisiana.  California, 

Specific  gravity 0.8646  0.8629  0.8621 

Refractive  index 1 .460  1 .4692  1 .4687 

Molecular  refraction: 

Found  for  C13H24 57.677  57.93  58.05 

Calculated 57.737  

Boiling-point,  755  mm 232  235 

28  mm 132  60  mm.      150 

Ultimate  composition: 

Carbon 86.48-86.56        86.58  86.68 

Hydrogen 13.28-13.15         13.42  13.62 

Calculated: 

Carbon 86.67 

Hydrogen 13 .33 

The  hydrocarbons  of  the  heavier  asphaltic  petroleums  are, 
therefore,  probably  bicyclic  or  bridge  compounds  in  those  of  lower 
boiling  point,  and  polycyclic  in  the  higher  ones. 

In  the  lightest  oils  from  Trinidad  asphalt  a  hydrocarbon  has 
been  isolated  which  has  the  same  formula  as  the  preceding  ones, 
but  differs  from  them  in  some  of  its  characteristics,  as  can  be  seen 
from  the  data  on  the  next  page. 

This  hydrocarbon,  while  in  some  respects  like  those  prepared 
by  synthesis  and  from  the  California  and  Louisiana  petroleums,  is 

J  Berichte  der  deutschen  chemischen  Gesellschaft,  1904,  37,  1667-1675. 
2  Coates,  J.  Am.  Chem.  Soc.,  1906,  384.    Mabery,  Proc.  Am.  Acad.,  1904, 
40,  340. 


108  THE  MODERN  ASPHALT  PAVEMENT. 

HYDROCARBON  FROM  TRINIDAD  ASPHALT. 

Specific  gravity 8690 

Refractive  index 1 .4721 

Molecular  refraction,  found 57 . 98 

' l  calculated 57 . 737 

Boiling-point,  30  mm 170-180° 

Ultimate  composition: 

Carbon 86 .85 

Hydrogen 13 .34 

sharply  differentiated  from  them  by  its  much  higher  boiling  point, 
and  cannot,  consequently,  be  of  the  same  structure.  The  as- 
phalt hydrocarbons  differ,  therefore,  from  those  found  in  the 
petroleums,  but  apparently  are  of  a  similar  nature,  and  the  low- 
est ones  at  least  of  the  series,  are  probably  substituted  bicyclic  or 
bridge  polymethylenes,  the  higher  being  polycyclic.  The  idea 
previously  advanced  by  Markownikoff,  Mabery  and  the  author 
that  they  were  probably  two  rings  united  by  polymethylene  groups, 
is  seen  to  be  untenable. 

Hydrocarbon  Derivatives. — Hitherto  hydrocarbons  only  have 
been  described  as  constituents  of  the  native  bitumens,  but  there 
are  other  substances  entering  into  their  composition  which  con- 
tain, in  addition  to  carbon  and  hydrogen,  sulphur,  nitrogen,  and 
more  rarely  oxygen.  They  consist  of  cyclic  compounds  contain- 
ing an  atom  of  sulphur  or  nitrogen  in  the  carbon  ring,  compounds 
which  are,  in  asphalt,  dicyclic  and  polycyclic,  and  oxygen  deriva- 
tives, probably  polycyclic  phenols,  together  with  oxidation  products 
of  the  hydrocarbons.  As  these  constitute  but  a  minor  portion 
of  native  bitumen  they  will  not  be  described  in  detail  here.  They 
can  be  readily  separated  from  the  hydrocarbons  by  appropriate 
reagents,  but  have  not  been  closely  studied.  They  are  also  found 
in  various  dense  petroleums. 

The  nature  and  structure  of  the  hydrocarbons  and  their  deriv- 
atives have  been  entered  into  with  some  detail  since  the  relative 
proportion  of  the  various  series  which  are  present  in  any  petro- 
leum or  solid  bitumen  has  a  strong  influence  on  its  characteristics, 
and,  more  especially,  the  relation  of  saturated  to  unsaturated 
hydrocarbons  and  of  the  paraffines  to  polymethylenes,  these  con- 
siderations being,  of  course,  quite  apart  from  the  relative  amounts 
of  liquid  and  solid  substances,  malthenes  and  asphaltenes,  upon 


NATURE  OF  THE  HYDROCARBONS.         109 

which  the  consistency  of  the  bitumen,  but  not  its  chemical  char- 
acteristics, are  based. 

The  saturated  hydrocarbons,  especially  those  of  the  paraffine 
series  which  are  found  in  the  residues  from  the  distillation  of 
Pennsylvania  petroleum  and  of  those  from  Ohio,  Kentucky,  Kansas, 
and  similar  oils,  are  most  stable.  They  are  not  readily  attacked 
by  strong  acids,  alkalies,  or  water  They  form  by  far  the  largest 
part  of  the  residuums  derived  from  these  petroleums.  The  satu- 
rated hydrocarbons  of  the  polymethylene  series  found  hi  some 
residuums  as  well  as  in  the  solid  bitumens  are  not  attacked  by 
acids  or  water,  but  are  readily  condensed  by  the  abstraction  of 
hydrogen  under  certain  other  conditions.  The  polymethylene 
hydrocarbons  or  the  petroleums  containing  them  are  in  this  way 
the  primary  source  of  all  asphalts.  No  asphalt  can  originate  in 
nature  in  a  paraffine  oil,  but  all  polymethylene  oils  leave  an  as- 
phaltic  residue  on  weathering  or  on  evaporation  or  distillation 
with  heat. 

No  solid  native  bitumen  suitable  for  paving  purposes  is  known 
which  contains  paraffine,  while  the  relative  proportions  of  satu- 
rated and  unsaturated  hydrocarbons  in  them  may  be  very  variable. 

The  characterization  of  heavy  oils  or  of  solid  bitumens  and 
their  differentiation  is,  therefore,  arrived  at  by  determining  by 
appropriate  analytical  methods  and  by  treatment  with  reagents 
the  relative  proportion  of  the  malthenes  and  asphaltenes  present, 
the  proportions  of  saturated  to  unsaturated  hydrocarbons  in 
the  malthenes,  and  the  characteristics  of  all  these  classes  of  bitu- 
mens. The  asphaltenes  are  probably  composed  entirely  of  unsat- 
urated or  unstable  compounds. 

SUMMARY. 

For  a  thorough  understanding  of  the  nature  of  the  native  bitu- 
mens the  constitution  of  the  various  hydrocarbons  of  which  they 
may  be  composed  has  been  outlined  in  the  preceding  chapter. 
This  involves  some  knowledge  of  chemistry  and  may,  therefore, 
be  somewhat  unintelligible  to  the  general  reader,  but  the  state- 
ments here  presented  are  entirely  necessary  in  any  treatise  which 
aims  at  being  at  all  complete  in  its  consideration  of  the  subject 
of  the  native  bitumens  and  of  asphalt  paving  mixtures. 


CHAPTER  VI. 

CHARACTERIZATION    AND    CLASSIFICATION    OF    THE    NATIVE 

.    BITUMENS. 

IN  a  recent  article  on  the  "  Bitumens  of  Cuba  "  the  author  has 
shown  that  while  there  have  been  numerous  attempts  to  define  the 
nature  of  bitumen,  and  to  characterize  and  classify  the  various  forms, 
none  of  them  has  been  satisfactory,  and  that  this  has  been  plainly 
due  to  the  fact  that  it  is  only  recently  that  a  sufficient  number 
of  deposits  have  been  studied  in  their  native  environment,  and 
in  the  laboratory,  by  methods  which  were  sufficiently  developed 
to  reveal  anything  as  to  the  constitution  of  the  harder  forms.  For 
example,  the  fact  that  hard  bitumen  in  the  form  of  asphalt  con- 
sists of  cyclic  polymethylenes  of  two  or  more  rings,  of  the  con- 
densation products  of  such  hydrocarbons  and  of  their  derivatives, 
and  that  this  form  of  bitumen  is  without  doubt  the  result  of  the 
metamorphism  of  cyclic  petroleums  by  natural  causes  has  only 
been  made  apparent  within  the  last  few  years. 

This  lack  of  data  to  serve  as  a  basis  of  comparison  and  char- 
acterization of  species,  and  as  an  aid  to  the  close  definition  of 
what  bitumen  is,  and  how  its  various  forms  can  be  differentiated, 
has  been  largely  supplied,  as  far  as  the  harder  forms — maltha, 
asphalt,  gilsonite,  grahamite,  albertite,  etc. — are  concerned,  by 
the  examination  in  the  author's  laboratory  of  several  hundred 
occurrences  of  these  materials,  scattered  over  the  greater  portion 
of  the  United  States  and  Canada,  the  West  Indies,  and  the  northern 
coast  of  South  America.  Our  knowledge  of  the  nature  of  various 
forms  of  petroleum  has  also  been  greatly  extended  by  the  work 
of  C.  F.  Mabery,  C.  E.  Coates,  E.  O'Neill,  and  numerous  con- 
tinental chemists,  and  that  of  natural  gas  by  F.  C.  Phillips  and 
others. 

There  is,  of  course,  a  vast  field  still  open  for  research,  but  it 

110 


NATIVE  BITUMENS.  Ill 

is  believed  that  the  presentation  of  the  subject  here  given  is  based 
on  more  complete  evidence  than  anything  heretofore  attempted. 

What  is  Bitumen? — The  most  rational  way  of  approaching 
the  question  appears  to  be  to  present  the  definitions  and  character- 
ization of  this  class  of  materials  as  a  whole,  and  then  of  the  par- 
ticular forms  as  they  may  be  differentiated  by  the  available  evi- 
dence; that  is  to  say,  to  put  the  results  which  have  been  reached 
before  the  reader,  and  then  to  show  how  these  have  been  arrived 
at  from  the  data  and  evidence  available. 

As  a  beginning,  bitumen  and  pyrobitumen  must  be  defined: 

Native  Bitumens  and  Pyrobitumens. — Native  bitumens  con- 
sist of  a  mixture  of  native  hydrocarbons  and  their  derivatives, 
which  may  be  gaseous,  liquid,  a  viscous  liquid  or  solid,  but,  if 
solid,  melting  more  or  less  readily  on  the  application  of  heat,  and 
soluble  in  turpentine,  chloroform,  bisulphide  of  carbon,  similar 
solvents,  and  in  the  malthas  or  heavy  asphaltic  oils.  Natural 
gas,  petroleum,  maltha,  asphalt,  grahamite,  gilsonite,  ozocerite, 
etc.,  are  bitumens.  Coal,  lignite,  wurtzilite,  albertite,  so-called 
indurated  asphalts,  are  not  bitumens,  because  they  are  not  soluble 
to  any  extent  in  the  usual  solvents  for  bitumen,  nor  do  they  melt 
at  comparatively  low  temperatures  nor  dissolve  in  heavy  asphaltic 
oils.  These  substances,  however,  on  destructive  distillation  give 
rise  to  products  which  are  similar  to  natural  bitumens,  and  they 
have  been  on  this  account  defined  by  T.  Sterry  Hunt  as  "  pyro- 
bitumens," which  differentiates  them  very  plainly  from  the  true 
bitumens.  They  usually  contain  oxygen,  whereas  the  true  bitu- 
mens, as  a  rule,  do  so  to  only  a  limited  extent. 

There  is,  of  course,  no  sharp  dividing  line  between  bitumens 
and  pyrobitumens,  as  the  former  are  gradually  metamorphosed 
by  tune  and  exposure  to  varied  environment  into  the  latter. 

Classifications  of  Bitumens. — Among  the  bitumens  there  are 
such  variations  in  physical  attributes  and  chemical  composition 
that  they  may  be  differentiated  as  follows: 
BITUMENS: 

GAS. 

Natural  hydrocarbon  gases. 
Marsh-gas. 


112  THE  MODERN  ASPHALT  PAVEMENT. 

PETROLEUM. 
Paraffine-oils. 

Consisting  of  hydrocarbons  and  their  derivatives,  the 
lower  members  of  which  belong  entirely  to  the 
paraffine  series  and  have  the  general  formula  CnH2n+2. 

(1)  Those    containing    CnH2n+2    hydrocarbons     up    to 
C2gH58  with  but  traces  of  sulphur  derivatives :  Penn- 
sylvania, West  Virginia,  Kentucky,  Kansas,  Colorado, 
etc. 

(2)  Those    containing    CnH2n+2  hydrocarbons    up   to 
CnH24  and  above  that  CnH2n  and   CnH2n-2  poly- 
methylenes   with   considerable   amounts   of   sulphur 
derivatives:   Ohio,  Canada. 

Cyclic  Oils. 

Consisting  principally  of  polymethylene  hydrocarbons 
of  the  series  CnH2n,  CnH2n_2  +  CnH2n_4,  together 
with  a  certain  amount  of  unsaturated  hydrocarbons 
and  their  derivatives. 

(1)  Stable  polymethylenes,  consisting   largely  of  naph- 
thenes,  CnH2n:   Russian  oils. 

(2)  Less  stable  polymethylenes  together  with  consider- 
able   amounts    of    unsaturated    hydrocarbons    and 
their  nitrogen  and  sulphur  derivatives,  and  leaving 
an  asphaltic  residue  on  distillation:    California. 

Oils  of  Mixed  Composition. 

Semi-asphaltic  oils  composed  largely  of  stable  paraffine 
and  polymethylene  hydrocarbons  not  readily  attacked 
by  sulphuric  acid:  Texas. 
MALTHA. 

Known  also  as  mineral  tar,  brea,  and  chapapote. 

Originating  from  polymethylene  petroleums  alone. 
Transition  products  between  oil  and  asphalt. 
SOLID  BITUMENS. 

Consisting  largely  of  paraffine  hydrocarbons. 

Ozocerite,  hatchettite,  etc. 

Consisting  of  unsaturated  cyclic  hydrocarbons. 
Ter -penes,  fossil  resins,  amber,  etc. 


NATIVE  BITUMENS.  113 

Derived    from    or    originating   in  polymethylene  petroleums, 
the  more  volatile  components  consisting  of  di-  or  tricyclic 
saturated  hydrocarbons. 
Asphalts. 

Asphalt.    Numerous  varieties:     Trinidad,  Venezuela,  Cali- 
fornia, Cuba. 
Glance  pitch. 
Consisting  largely  of  cyclic  hydrocarbons  attacked  by  strong 

sulphuric  acid,  but  which  otherwise  are  stable. 
Manjak. 

Yielding  high  fixed  carbon  and  a  black  powder. 
Gilsonite. 

Yielding  average  fixed  carbon  and  a  brown  powder,  .the 
more  volatile  components  resembling  sticky  oleo  resins 
rather  than  hydrocarbons  found  in  the  asphalts. 
Grahamite. 

Consisting  of  hydrocarbons  almost  entirely  insoluble  in 
naphtha  and  yielding  a  higher  percentage  of  fixed  carbon 
on  ignition.     Melting  with  difficulty. 
The  grahamites  rapidly  shade  into  pyrobitumens. 
PYROBITUMENS: 

Practically  insoluble  in  chloroform  or  heavy  petroleum  hydro- 
carbons. 

Derived  from  petroleum, 
Albertite,  with  varieties  called  nigrite,  etc. 
Wurtzilite. 

Derived  from  direct  metamorphoses  of  vegetable  growth. 
Anthracite. 
Bituminous  coal. 
Lignite. 
Peat  (?). 

Of  the  bitumens,  as  we  have  seen,  the  hard  ones  and  the 
oils  enter  into  the  composition  of  paving  cements  and 
must  be  considered  individually. 

SUMMARY. 

The  author's  classification  of  the  native  bitumens  and  those 
of  other  writers  are  unfortunately  founded  on  an  empirical  basis 


114  THE  MODERN  ASPHALT  PAVEMENT. 

to  too  great  a  degree  to  admit  of  their  being  satisfactory  to  every 
one.  Such  classifications  can  be  regarded  as  mere  steps  toward 
a  final  conclusion  which  can  only  be  arrived  at  after  years  of 
investigation  of  the  subject.  The  author's  classification  is  pre- 
sented for  what  it  is  worth,  and  there  will  be  no  hesitation  in 
modifying  it  in  the  future  in  the  light  of  any  additional  informa- 
tion which  may  become  available  which  is  based  on  facts  and 
not  on  mere  opinion  or  theory.  For  a  thorough  understanding 
of  the  character  of  the  native  bitumens  it  is  advisable  that  the* 
general  reader  should  acquaint  himself  with  the  peculiarities  01 
the  different  classes  which  it  has  been  possible  to  differentiate, 
the  one  from  the  other,  in  order  that  an  intelligent  understanding 
may  be  arrived  at  of  the  very  variable  nature  of  the  bitumens  in 
use  in  the  asphalt  paving  industry. 

The  mere  minute  differences  in  the  various  bitumens,  upon 
which  their  differentiation  has  been  based,  will  be  made  plain  in 
the  following  pages. 


PAET  III. 

NATIVE  BITUMENS  IN   USE  IN  THE  PAVING 
INDUSTRY. 


INTRODUCTION. 

IN  the  light  of  the  preceding  classification  of  the  native  bitumens 
and  our  knowledge  of  the  various  series  of  hydrocarbons  of  which 
they  are  composed  the  characteristics  of  the  fluxes,  the  asphalts, 
and  other  solid  native  bitumens  in  use  in  the  paving  business 
may  now  be  taken  up. 


CHAPTER  VII. 

DIFFERENTIATION  AND  CHARACTERIZATION  OF  THE  NATIVE 

BITUMENS. 

ALL  the  native  bitumens  are  such  complicated  mixtures  of 
various  hydrocarbons  and  their  derivatives  that  it  is  impossible 
to  separate  them  completely  into  their  individual  constituents 
and  to  differentiate  and  characterize  them  in  this  way.  Recourse 
must,  therefore,  be  had  to  the  determination  of  their  physical 
properties  and  to  attempts,  more  or  less  successful,  to  separate 
the  proximate  constituents  of  which  they  are  made  up  into  various 
classes  according  to  their  solubility  and  behavior  towards  reagents, 
supplemented  by  the  determination  of  the  amount  of  fixed  carbon 
which  they  yield  on  ignition  and  their  ultimate  composition. 

Physical  Properties. — The   physical   properties   which   are   of 

value  in  characterizing  the  bitumens  are: 

115 


116  THE  MODERN  ASPHALT  PAVEMENT. 

SOLID  BITUMENS. 

PHYSICAL   PROPERTIES. 

Specific  gravity,  78°  F./780  F.   Original  substance,  dry 

' '  "  "  Pure  bitumen 

Color  of  powder  or  streak 

Lustre 

Structure 

Fracture. 

Hardness,  original  substance 

Odor 

Softens 

Flows 

Consistency,  penetration  at  78°  F 

The  chemical  characteristics  of  interest  are: 

CHEMICAL    CHARACTERISTICS. 

Original  substance 

Loss,  212°  F.,  1  hour 

Dry  substance 

Loss,  325°  F.,  7  hours 

Character  of  residue 

Consistency,  penetration  of  residue  at  78°  F 


Loss,  400°  F. ,  7  hours  (fresh  sample) 

Character  of  residue 

Consistency,  penetration  of  residue  at  78°  F. 


Bitumen  soluble  in  CS2,  air  temperature 

Inorganic  or  mineral  matter 

Difference  . . 


Malihenes: 

Bitumen  soluble  in  88°  naphtha,  air  temperature . . , 

This  is  per  cent  of  total  bitumen 

Per  cent  of  soluble  bitumen  removed  by  H2SO4  .... 
Per  cent  of  total  bitumen  as  saturated  hydrocarbons. 

Bitumen  soluble  in  62°  naphtha 

This  is  per  cent  of  total  bitumen 

Carbenes: 

Bitumen  insoluble  in  carbon  tetrachloride,  air  tem- 
perature   

Bitumen  yields  on  ignition : 

Fixed  carbon.  .  . 

Sulphur 

Ultimate  composition 


NATIVE  BITUMENS.  117 


FLUXES. 

PHYSICAL   PROPERTIES. 

Specific  gravity,  dried  at  212°  F.,  78°  F./780  F. 

Flows,  cold  test 

Color    

Odor.  .  . 

Under  microscope 

Flashes,  °  F.,  N.  Y.  State  oil-tester '. 

Viscosity  P.R.R.  pipette  at  -  °  F. . , 


CHEMICAL   CHARACTERISTICS. 

Original  substance 

Loss,  212°  F.,  1  hour  or  until  dry 

Dry  substance 

Loss,  325°  F.,  7  hours 

Character  of  residue 

Penetration  of  residue  at  78°  F.  . 


Loss,  400°  F.,  7  hours  (fresh  sample). 

Character  of  residue 

Penetration  of  residue  at  78°  F.  . 


Bitumen  soluble  in  CS2,  air  temperature. 

Inorganic  or  mineral  matter 

Difference  .  . 


Bitumen  insoluble  in  88°  naphtha,  air  temperature, 

pitch 

Per  cent   of  soluble  bitumen  removed  by  H.jSO4 

Per  cent  of  total  bitumen  as  saturated  hydrocarbons 

Per  cent  of  solid  paraffines 


Fixed  carbon 

Ultimate  composition. 


Specific  Gravity.  —  For  the  physical  characteristics  it  may  be 
said  that  the  specific  gravity  of  the  solid  bitumens  as  they  are 
originally  found  in  nature  will  depend  very  largely  upon  the  per- 
centage of  mineral  matter  which  they  contain.  One  like  Trinidad 
lake  asphalt,  containing  37  per  cent  of  mineral  matter,  will  have 
a  specific  gravity  of  1.40,  while  an  extremely  pure  bitumen,  like 
gilsonite,  will  have  a  specific  gravity  of  1.04. 


118  THE  MODERN  ASPHALT  PAVEMENT. 

Where  the  pure  bitumen  is  extracted  from  the  native  material 
the  density  will  not,  as  a  rule,  vary  very  widely.  For  the  asphalts 
it  will  lie  between  1.03  to  1.07. 

Ozocerite  is  the  only  solid  bitumen  which  has  a  specific  gravity 
below  1.00,  .912,  while  grahamite,  albertite,  and  glance  pitch 
exceed  a  density  of  1.09. 

The  density  of  the  residual  pitches,  at  least  of  those  met  in 
the  paving  industry,  is  usually  quite  similar  to  that  of  the 
bitumens  of  the  native  asphalts,  not  rising  above  1.1,  unless  in 
their  preparation  they  have  been  carried  to  a  very  high  tem- 
perature, nor  falling  below  1.0  if  they  are  at  all  solid.  Some  of 
the  condensed  oils,  such  as  Byerlyte,  Pittsburg  flux,  and  blown 
asphaltic  oil,  have  a  density  below  1.0  and  can  be  recognized  by 
the  fact  that  they  float  on  water. 

The  specific  gravity  of  the  various  bitumens  is,  therefore,  of 
some  considerable  interest. 

A  summary  of  some  of  the  data  collected  by  the  author  is 
given  in  the  following  table: 

Substance.  Specific  Gravity. 

Trinidad  lake  refined  asphalt 1 . 4000 

land      "  "      1.4196 

Bermudez  refined  asphalt— 1900 1 .0823 

11      —1903 1.0575 

Maracaibo  refined  asphalt.  . 1 . 0667 

Cuban  (Bejucal)  asphalt 1 .3050 

Mexico— Tamesi  River  asphalt  (dry) 1 .1180 

11      — chapapote  asphalt  (dry) 1 .0450 

California — La  Patera 1 . 3808 

"       —Standard,  refined 1 .0627 

Utah— gilsonite  firsts 1 .0433 

"    -          "        seconds 1 .0457 

Grahamite — Indian  Territory,  Ten  Mile  Creek. .  1 . 1916 

—Colorado,  Middle  Park 1 . 1600 

Egyptian  glance  pitch ' 1 . 0970 

Manjak 1 .0844 

Ozocerite— Utah 0 .9123 

Albertite— Nova  Scotia 1 .0790 

"       —Utah 1 .0990 

"       —Cuba 1 .2040 

Wurtzilite— Utah 1 .0556 

Kentucky,  Grayson  Co. — seepage 0.9783 


NATIVE  BITUMENS.  119 

Substance.  Specific  Gravity. 

Utah,  Soldier  Creek — extracted  bitumen 1 .2000 

"      Grand  Co. — extracted  bitumen 1 .0370 

"D"  grade  Calif orina,  carefully  prepared 1 .0622 

carelessly       "        ....  1.0887 

Asph.  O.&Ref.  Co....  1.0770 

Beaumont,  Texas,  oil  asphaltic  residue 1 .0803 

Baku  pitch  from  Russian  petroleum 1 . 1098 

Pittsburg  flux 0 .9879 

Ventura  flux 1 .0199 

Byerlyte,  paving 1 .0230 

roofing 0.9070 

Hydroline  "B" 1 .0043 

Color  of  Powder  or  Streak. — Where  the  solid  native  bitumens 
are  sufficiently  hard  to  permit  of  their  being  powdered  or  to  make 
a  streak  upon  porcelain,  the  color  of  the  powder  or  streak  may 
be  of  some  value  in  differentiating  them.  For  example,  the  powder 
of  refined  Trinidad  lake  asphalt  is  of  a  bluish-black  color,  whereas 
that  of  Trinidad  land  asphalt  is  distinctly  brown.  Most  of  the 
asphalts  give  a  powder  of  either  a  dull-black  or  brownish-black 
color,  but  gilsonite  is  distinguished  by  its  extreme  brittleness  and 
the  fact  that  the  powder  is  of  an  extremely  light-brown  color. 

Lustre. — All  the  native  bitumens  are  lustrous  if  pure,  with 
the  exception  of  ozocerite.  The  residual  pitches  are,  of  course, 
lustrous.  In  the  presence  of  mineral  matter  the  lustre  is  more 
or  less  diminished,  depending  upon  the  amount  of  the  latter. 

Structure. — The  structure  of  the  native  bitumens  is  in  many 
cases  very  characteristic.  To  begin  with,  it  is  either  uniform 
and  homogeneous  in  every  part  or  the  reverse.  In  crude  Trinidad 
lake  asphalt  we  note  the  presence  of  gas  cavities  and  of  emul- 
sified water.  In  some  California  asphalts  large  particles  of  brec- 
ciated  shale  are  scattered  through  the  native  asphalt,  which  occurs 
in  veins.  On  the  other  hand,  gilsonite  is  of  an  extremely  uniform 
structure  except  where  the  material  approaches  the  vein  wall, 
where  it  at  times  takes  on  a  columnar  structure  due  to  weather- 
ing. Glance  pitch  and  manjak  are  also  of  extremely  uniform 
structure.  The  same  thing  may  be  said  in  regard  to  many  refined 
asphalts  in  which  the  lack  of  homogeneity  has  been  removed  by 
melting.  The  structure  of  the  residual  pitches  is,  of  course,  quite 


120  THE  MODERN  ASPHALT  PAVEMENT. 

homogeneous,  except  where  they  may  have  been  coked  to  a  cer- 
tain degree  by  excessive  heating. 

Fracture. — The  fracture  of  the  native  solid  bitumens  in  many 
cases  is  as  characteristic  as  the  structure.  Almost  all  grahamites, 
although  homogeneous  in  structure,  have  a  peculiar  fracture  which 
distinguishes  them  from  all  the  other  solid  bitumens.  It  has 
been  described  as  a  hackley  or  pencilated  fracture,  which,  perhaps, 
covers  it  sufficiently.  It  is  an  irregular  fracture  and  shows  no 
evidence  of  a  purely  lustrous  surface,  as  in  the  fracture  of  gilsonite. 
The  fracture  of  crude  Trinidad  asphalt  is  quite  irregular,  that  of 
gilsonite  conchoidal  and  highly  lustrous,  while  that  of  many  refined 
asphalts  is  only  semi-conchoidal. 

Hardness. — The  hardness  of  the  native  bitumens  in  the  form 
in  which  they  originally  occur  may  be  stated  in  terms  of  Mohr's 
scale.  Where  the  pure  bitumen  is  softer  than  1  of  this  scale,  it 
may  be  stated  in  terms  of  one  of  the  various  penetration  machines. 

Odor. — The  odor  of  most  of  the  native  bitumens  is  character- 
istic at  ordinary  temperatures.  The  asphalts  have  in  general 
an  asphaltic  odor,  but  some  of  them,  such  as  that  from  near  the 
Gulf  of  Maracaibo,  in  Venezuela,  are  characteristically  rank.  Gil- 
sonite has  scarcely  any  perceptible  odor,  while  the  residual  pitches 
have  a  peculiar  oily  odor.  On  heating,  stronger  odors  are  com- 
monly developed  which  are  recognizable  to  one  accustomed  to 
them,  but  the  nature  of  which  is  difficult  to  describe  in  print. 

Softening  and  Flowing  Points. — The  native  bitumens  possess 
no  melting-point.  It  can  be  stated  that  they  are  in  a  melted 
condition  at  such  and  such  a  temperature,  but  since  they  are 
made  up  of  a  mixture  of  hydrocarbons  and  their  derivatives  it 
is  impossible  for  them  to  have  a  true  melting-point,  such  as  that 
of  ice  or  any  definite  compound.  In  cooling  a  mass  of  water  in 
which  a  thermometer  is  immersed  from  any  temperature,  say  50°  F., 
to  a  point  below  freezing  and  representing  this  on  a  system  of 
coordinates,  the  time  being  denoted  by  the  abscissae  and  temper- 
ature by  the  ordinates,  a  curve  will  be  developed  which  at  the 
point  of  freezing,  while  the  water  is  being  converted  into  ice,  is 
broken  by  a  straight  line  which  denotes  the  tune  during  which 
the  liquid  is  becoming  converted  to  ice.  If  any  native  bitumens 


NATIVE  BITUMENS.  121 

are  melted  and  cooled  in  the  same  way  no  definite  break  corre- 
sponding to  any  definite  freezing-point  is  detected.  It  is,  therefore, 
impossible  for  us  to  speak  of  the  melting-point  of  a  bitumen,  but 
we  may  determine  in  any  empirical  way  the  point  at  which  any 
solid  bitumen  softens  and  again  when  it  flows,  as  specified  in  the 
author's  method  given  in  Chapter  XXVIII.  The  determinations 
of  this  nature  given  in  the  following  pages  were  made  in  this  way. 
Chemical  Characteristics. — It  will  be  noted  that  in  the  differen- 
tiation of  the  bitumens  into  classes  by  means  of  solvents,  certain 
names  have  been  applied  to  the  various  classes  of  hydrocarbons. 
In  the  early  days  of  the  study  of  the  behavior  of  solvents  towards 
native  bitumens,  the  various  hydrocarbons  and  their  derivatives 
were  differentiated,  according  to  their  solubility  in  naphtha,  into 
classes  to  which  the  names  "  Petrolene "  and  "  Asphaltene," 
terms  used  by  Boussingault  in  his  earliest  investigations,  were 
applied.  These  terms  were  open  to  the  objection  that  it  led  per- 
sons not  thoroughly  acquainted  with  the  chemistry  of  the  natural 
hydrocarbons  to  believe  that  petrolene  and  asphaltene  were 
definite  compounds,  which,  of  course,  is  no  more  the  case  than  to 
assume  that  the  oil  known  under  the  name  kerosene  is  a  definite 
compound.  The  author,  therefore,  changed  the  designation  to 
"  Petrolenes "  and  "  Asphaltenes "  as  more  plainly  indicating 
that  the  differentiation  was  merely  one  of  classes.  More  recently 
it  has  seemed  possible  to  carry  the  differentiation  still  further, 
since  it  has  been  found  that  the  solubility  of  the  native  bitumens 
in  cold  carbon  tetrachloride  is  not  in  all  cases  the  same  as  in  bisul- 
phide of  carbon  or  chloroform  and  that  solubility  or  insolubility 
in  this  medium  can  be  added  to  those  previously  employed  for 
this  purpose.  Peckham  has  also  shown  that  chloroform  dissolves 
hydrocarbons  which  are  not  soluble  hi  carbon  disulphide,  and 
this  solvent  may  be  added  to  our  list,  or  even  oil  of  turpentine 
if  thought  necessary.  The  author's  idea  in  regard  to  the  future 
differentiation  of  the  native  bitumens  would  involve  the  applica- 
tion of  the  term  "  Malthenes,"  to  the  bitumens  soluble  hi  naphtha 
in  place  of  the  term  "  Petrolenes,"  stating  the  specific  gravity 
of  the  naphtha  used  as  a  solvent,  as  this  class  of  bitumens  bears  a 
great  resemblance  to  the  malthas;  reserving  the  term  "  Petrolenes  " 


122  THE  MODERN  ASPHALT  PAVEMENT. 

for  those  hydrocarbons  which  are  volatile  at  325°  F.  in  7  hours, 
according  to  the  author's  method,  these  hydrocarbons  being  com- 
paratively light  oils  resembling  ordinary  petroleum.  He  would 
characterize  as  "  Asphaltenes "  those  hydrocarbons  and  their 
derivatives  which  are  soluble  in  cold  carbon  tetrachloride  and 
as  "  Carbenes  "  those  not  soluble  in  cold  carbon  tetrachloride, 
but  soluble  in  carbon  disulphide.  This  differentiation  has  not 
been  carried  out  in  the  author's  work  to  any  great  extent  in  the 
past,  but  in  many  cases  in  the  following  tables  the  percentage  of 
the  bitumen  insoluble  in  cold  carbon  tetrachloride  will  be  found 
to  prove  of  great  interest. 

In  the  determination  of  the  amount  of  fixed  carbon  which  any 
native  bitumen  will  yield  when  heated  to  a  high  temperature  in 
the  absence  of  oxygen,  after  the  manner  proposed  for  making  the 
same  determination  in  coal,  data  are  obtained  which  are  of  great 
interest  as  showing  the  relative  proportion  of  carbon  and  hydrogen 
in  the  bitumen  under  examination.  In  the  case  of  the  parafnne 
hydrocarbons  of  the  formula  CnH2n+2  no  fixed  carbon  is  left  on 
ignition,  while  the  amount  increases  with  each  diminution  in  the 
proportion  of  hydrogen  to  carbon,  until  in  grahamite  as  much 
as  50  per  cent  is  found,  where  the  relation  of  carbon  to  hydrogen 
is  as  8  to  1. 

The  ultimate  composition  of  the  bitumens  is,  of  course,  of 
interest,  but  for  general  purposes  the  information  derived  from 
this  determination  seldom  repays  the  time  and  care  necessary. 

The  methods  employed  in  arriving  at  the  results  which  are 
presented  in  the  following  tables  are  given  hi  a  later  chapter  of 
this  book,  and  reference  must  be  made  to  it  for  the  details  of  the 
process  and  for  a  thorough  understanding  of  what  each  deter- 
mination may  mean.1 

It  will  be  found  on  examining  these  methods  that  the  results 
obtained  by  their  use  are  in  no  sense  absolute  determinations, 
but  when  each  of  the  asphalts  is  treated  in  quite  the  same  way 
as  the  others  they  are  of  great  value  relatively  and  for  purposes 
of  comparison  and  differentiation.  In  regard  to  certain  of  the 
data  some  explanation  will  be  necessary. 

1  Page  519. 


NATIVE  BITUMENS.  123 

Bitumen  Soluble  in  Bisulphide  of  Carbon,  Air  Temperature. — This 
determination  shows  the  amount  of  bitumen  which  is  soluble  in  cold 
bisulphide  of  carbon.  If  hot  bisulphide  of  carbon,  chloroform,  or 
turpentine  and  in  some  exceptional  cases  hot  carbon  tetrachloride 
are  used  as  a  solvent,  a  slightly  larger  percentage  would  probably  be 
found  but,  owing  to  the  difficulties  in  maintaining  uniform  conditions 
for  extraction  at  other  than  ordinary  temperatures  and  for  other 
reasons  which  it  is  unnecessary  to  specify  here,  cold  bisulphide 
of  carbon  has  been  used  and  the  results  obtained  are  more  satis- 
factory for  comparative  purposes  than  would  otherwise  be  the 
case. 

Inorganic  Matter. — The  determination  of  inorganic  or  mineral 
matter  represents  the  residue  remaining  on  the  ignition  of  the 
native  bitumen  in  a  muffle  at  such  a  temperature  as  to  remove 
all  the  carbon.  In  certain  cases  the  amount  obtained  may  be 
less  than  that  originally  present,  owing  to  the  volatilization  of 
alkalies  or  sulphuric  acid,  but  it  is  sufficiently  accurate  for  pur- 
poses of  comparison. 

Insoluble  or  Difference. — On  adding  together  the  percentages 
of  bitumen  soluble  in  carbon  disulphide  and  of  inorganic  matter 
obtained  on  ignition,  the  sum  will  seldom  amount  to  100.0.  The 
difference  which  is  stated  as  such  in  our  analyses  has  for  many 
years  been  considered  as  organic  matter  not  bitumen.  This  may 
be  true  in  exceptional  cases,  but  recent  investigations1  have  shown 
that  it  is  not  at  all  so  in  many  bitumens.  For  example,  in  Trinidad 
asphalt  it  has  been  found  to  consist  of  the  water  of  combination  of 
the  clay  which  the  material  contains  and  some  inorganic  salts  which 
are  volatilized  on  ignition.  The  amount  of  organic  matter  is 
extremely  small.  In  other  cases,  it  may  consist  to  a  considerable 
extent  of  grass  and  twigs,  as  in  the  seepages  which  have  run 
out  over  sod.  On  the  whole,  therefore,  it  seems  desirable  not  to 
describe  it  by  any  definite  name,  but  merely  as  an  undetermined 
difference. 


1  Proc.  Am.  Soc.  Test.  Mat.,  1906,  6,  509. 


124  1HE    MODERN    ASPHALT    PAVEMENT. 

Loss  at  825°  F.  in  7  hours. — The  hydrocarbons  lost  at  325°  F., 
which  the  author  has  proposed  to  denominate  "  Petrolenes,"  as  a 
class,  will  vary  in  amount  enormously  according  to  the  conditions 
under  which  the  heating  is  carried  out.  When  these  are  accu- 
rately defined,  however,  as  in  our  methods,  the  relative  loss  is 
an  important  indication  in  differentiating  any  two  bitumens. 

Malthenes. — It  is  a  well-known  fact  that  the  percentage  of 
malthenes  or  bitumen  soluble  in  naphtha  will  vary  according  to 
the  solvent  used,  and  in  the  case  of  naphtha  if  its  density  is  low, 
according  to  the  method  by  which  the  solvent  is  applied.  In 
the  determinations  given  in  the  table  naphthas  of  a  definite  density, 
88°  and  62°  Beaume,  have  been  allowed  to  act  on  the  native  bitu- 
men, in  as  finely  a  comminuted  condition  as  possible,  in  the  cold 
for  a  definite  length  of  time  and  the  residue  washed  quite  clean 
with  the  same  solvent.  Had  the  solvent  been  applied  warm  or 
in  a  continuous  percolation  apparatus  the  figures  would  have 
been  higher  but  would  not  have  been  constant,  since  the  lighter 
hydrocarbons  in  the  solvent  would  have  been  gradually  volatilized 
and  their  solvent  power  slowly  increased.  For  comparative  pur- 
poses the  method  in  use  is  more  satisfactory  than  any  other,  but 
the  results  themselves  are  of  no  value  as  an  absolute  differentiation 
of  the  native  bitumen  into  two  definite  classes  of  materials. 

Action  of  Strong  Sulphuric  Acid  on  the  Hydrocarbons. — The 
results  presented  showing  the  action  of  strong  sulphuric  acid  on 
the  hydrocarbons  soluble  in  88°  naphtha  are  only  of  value  because 
all  of  them  are  carried  out  according  to  a  definite  and  arbitrary 
method.  If  this  were  varied  the  results  would  also  vary.  It  is 
important  to  know  that  strong  sulphuric  acid  has  a  somewhat 
different  action  on  the  hydrocarbons  of  a  solid  bitumen  if  it  is 
allowed  to  act  on  an  88°  or  62°  naphtha  solution  of  them.  In 
the  62°  naphtha  solution  the  action  is  apparently  much  less  than 
in  the  solution  of  the  solvent  of  lighter  density. 

Bitumen  Insoluble  in  Carbon  Tetrachloride,  Air  Temperature. — 
The  amount  of  bitumen  soluble  in  cold  carbon  tetrachloride,  in  all 
the  normal  asphalts,  is  practically  the  same  as  that  soluble  in 
carbon  disulphide,  but  in  certain  native  bitumens  hydrocarbons  are 


NATIVE  BITUMENS.  125 

found  which  are  insoluble  in  this  medium.  This  differentiates  these 
bitumens — grahamite,  for  example — from  the  true  asphalts,  the 
insoluble  bitumen  forming  a  class  of  hydrocarbons  or  of  their 
derivatives  to  which  the  name  of  "  Carbenes  "  has  been  applied. 
Such  bitumens  have  evidently  been  much  more  metamorphosed 
by  weathering  or  otherwise  than  the  true  asphalts,  or  have  orig- 
inated in  a  different  series  of  hydrocarbons. 

In  residual  pitches,  at  tunes  some  of  the  bitumen  is  found 
which  is  insoluble  in  cold  carbon  tetrachloride,  and  this  is  evi- 
dently due  to  the  severe  treatment  which  the  material  has  suffered 
in  the  course  of  its  production  at  very  high  temperatures.  •  A 
determination  of  the  amount  is  only  valuable  as  an  indication 
of  the  care  which  has  been  used  in  the  preparation  of  such  pitches. 
In  the  best  asphaltic  residues  from  California  petroleum  the  per- 
centage of  "  Carbenes  "  has  been  found  to  vary  from  7  to  less 
than  one-half  of  1  per  cent. 

Fixed  Carbon. — The  amount  of  fixed  carbon  which  any  solid 
native  bitumen  will  yield  will  depend,  as  in  the  case  of  coal,  upon 
the  way  in  which  the  material  is  ignited.  All  the  deteYmina- 
tions  given  have  been  made  by  following  the  'scheme  suggested 
by  the  Committee  of  the  American  Chemical  Society  on  the  Analysis 
of  Coal,  and  are,  therefore,  strictly  comparable. 

With  these  facts  in  view  the  analyses  of  the  native  bitumens 
which  are  to  be  presented  will  be  of  interest  for  the  purpose  of 
comparing  the  characteristics  of  the  various  materials,  but  the 
chemical  data  must  not  be  looked  upon  as  being  absolute  in  any 
case. 

SUMMARY. 

By  determining  the  physical  characteristics  of  any  native 
bitumen,  its  specific  gravity,  its  color  hi  a  powdered  condition, 
its  lustre,  structure,  fracture,  hardness,  odor,  softening  point, 
and  consistency,  by  differentiating  the  bitumen  into  various  classes 
of  hydrocarbons  by  means  of  solvents  and  by  observing  certain 
other  chemical  characteristics,  such  as  the  ultimate  composition, 
the  amount  of  fixed  carbon  left  on  ignition,  and  the  extent  to 
which  the  hydrocarbons  of  which  it  is  composed  are  acted  upon 


126  THE    MODERN    ASPHALT    PAVEMENT. 

by  strong  sulphuric  acid,  it  is  quite  possible  to  characterize  and 
classify  the  various  native  bitumens  in  such  a  way  as  to  make  it 
possible  to  recognize  them  without  difficulty  and  without  con- 
fusing one  with  another.  The  methods  for  making  these  deter- 
minations appear  in  Chapter  XXVIII. 


CHAPTER  VIII. 
PETROLEUMS. 

IN  the  asphalt  paving  industry  the  petroleums  are  of  interest 
because  the  heavier  hydrocarbons  or  residuum  which  remains 
on  distilling  off  the  lighter  portion  of  the  oil  are  used  as  a  flux 
for  the  solid  native  bitumens.  The  character  of  these  residuums 
and  fluxes  reflects,  of  course,  the  nature  of  the  petroleum  from 
which  they  have  been  made,  the  paraffine  oils  yielding  a  residuum 
of  one  kind,  the  asphaltic  oils  one  of  another,  and  the  mixed  par- 
affine and  asphaltic  oils,  such  as  those  from  the  Beaumont  field 
and  elsewhere  in  Texas  and  from  Oklahoma  and  part  of  Kansas, 
one  of  quite  another  character. 

For  a  more  definite  knowledge  of  the  proximate  composition 
of  various  petroleums,  beyond  that  which  has  been  given  in  the 
classification,  reference  must  be  made  to  the  publications  of  those 
who  have  devoted  their  tune  to  a  study  of  this  subject,  among 
whom  may  be  named  Mabery,  Young,  Markownikoff,  and  Engler. 
Unfortunately  the  publications  of  these  investigators  are  widely 
scattered  and  appear  nowhere  hi  condensed  form.  Their  general 
conclusions  have  been  included  hi  the  author's  classification 
of  petroleums. 

Malthas. — The  malthas  are  viscous  liquid  natural  bitumens  cor- 
responding hi  consistency  to  that  of  the  artificial  residuums  or  usually 
denser.  They  are  only  rarely  of  a  suitable  character  for  use  as  a 
flux,  owing  to  the  fact  that  on  heating  they  are  generally  rapidly 
converted  into  a  harder  material  by  the  loss  of  volatile  hydro- 
carbons and  condensation  of  the  molecule.  It  was  due  to  this 
fact  that  the  early  pavements  laid  with  Alcatraz  asphalt  were 
not  successful.  The  flux  in  use  was  a  natural  maltha  derived 
from  the  Carpinteria  sands,  which,  while  of  the  proper  consistency 

127 


128  THE   MODERN   ASPHALT  PAVEMENT. 

as  prepared,  was  rapidly  converted  into-  a  solid  bitumen  on  pro- 
longed heating. 

The  bitumen  in  the  Kentucky  sands  is  much  more  of  the  nature 
of  a  maltha  than  of  an  asphalt,  and  it  is  on  this  account  that  these 
materials  are  unsatisfactory  for  paving  purposes  in  addition  to 
the  fact  that  they  contain  usually  a  much  too  small  percentage 
of  bitumen. 

For  the  above  reasons  the  native  malthas  are  rarely  used  in 
the  preparation  of  asphalt  cement  and.  never  with  successful 
results. 

On  page  129  are  given  some  examples  of  the  characteristics  of 
malthas  from  various  parts  of  the  world. 

It  appears  that  the  malthas  may,  when  dry  but  not  otherwise 
altered,  have  a  specific  gravity  either  less  or  greater  than  water. 
They  all  volatilize  a  very  considerable  amount  of  light  oils  at 
325°  F.,  and  most  of  them  large  amounts  at  400°  F.  In  the  case 
qf  four  out  of  nine  of  those  cited  the  residue  after  heating  to  only 
325°  F.  was  hard  enough  to  permit  a  determination  of  their  con- 
sistency with  the  penetration-machine.  Under  the  same  circum- 
stances a  paraffine  residuum  would  still  remain  a  flux,  as  would 
the  best  asphaltic  petroleum  residuums.  They  frequently  contain 
notable  percentages  of  the  asphaltenes  and  all  become  pitch  after 
heating  to  a  constant  weight  at  400°  F. 

The  Residuums  of  Petroleums  Used  as  Fluxes  in  Softening 
the  Solid  Native  Bitumens. — In  order  to  bring  the  solid  native 
bitumens  to  such  a  consistency  as  will  make  them  available  for  use 
as  a  paving-cement  it  is  generally  necessary  to  flux  them  with 
some  other  softer  bitumen.  The  flux  in  use  for  this  purpose  is 
uniformly  a  heavy  residuum  prepared  by  the  removal  of  the  lighter 
portions  of  petroleum  by  distillation.  These  residues  naturally 
vary  in  character  in  the  same  way  that  the  petroleums  do  from 
which  they  have  been  derived,  and  that  the  petroleums  are 
very  variable,  depending  upon  the  series  of  hydrocarbons  of  which 
they  are  composed,  has  already  been  made  evident.  The  oils  from 
which  residuums  or  fluxes  are  prepared  for  use  in  the  United  States 
are  the  paraffine  petroleums  from  the  Eastern,  Ohio,  Kentucky, 
Kansas,  Oklahoma,  and  Colorado  fields,  the  asphaltic  petro- 


PETROLEUMS. 


129 


Characteristics  of  Malthas. 

Test  No. 

30374. 

California, 
Sunset 
District. 

30116. 

California, 
McKitrick 
District. 

25129. 

Cuba, 
Hato 
Nuevo. 

50912. 

Cuba, 

Matanzas. 

Loss   212°  F 

270°  F. 

.9884 
12.4% 

16.1% 

* 

7.76% 

11.0% 
325°  F. 

1.0029 
8-9% 

13.2% 

22.8% 

32.1% 
16° 

17.6% 
8.1% 
8.6% 

245°  F. 

.9867 
7.0% 

28.0% 
40° 

DRY    SUBSTANCE. 

Specific  gravity,  78°  F./780  F. 
Loss  325°  F    7  hours    .  .  . 

.9445 

5.8% 
38° 

Penetration  of  residue  at  78°F. 
Loss  400°  F  ,  7  hours  

Penetration  of  residue 

Loss  325°  F  to  constant  wt 

Penetration  of  residue 

Loss,  400°  F.  to  constant  wt  . 

Bitumen    insoluble    in    88° 
naphtha,  pitch  

6.7% 

25.5% 
15.7% 

Bitumen    insoluble    in    62° 
naphtha  pitch 

Bitumen  yields  on  ignition  : 
Fixed  carbon                .... 

Test  No. 

Characteristics  of  Malthas. 

39556. 

Venezuela, 
Peder- 
nales. 

10106. 

Venezuela, 
Mene 
River. 

63846. 

Texas, 
Austin. 

30283. 

Trinidad, 
Boodoo- 
shingh. 

60487. 

Trinidad, 
Mara- 
bella. 

Loss,  212°  F  

9.7% 

9.0% 

1.5% 

18.5% 

5.2% 

Flash-point                     

DRY    SUBSTANCE. 

Specific  gravity  78°  F./780  F. 
Loss,  325°  F.,  7  hours  
Penetration  of  residue  at  78°F. 
Loss,  400°  F  ,  7  hours     .    .  . 

1.032 

4.6% 
75° 
11  1% 

8^5% 
5  9% 

.974 
7.1% 

17  0% 

10^% 
hard 

6-  '4% 
32° 
10  3% 

Penetration  of  residue  

23° 

* 

20° 

Loss,  325°  F  to  constant  wt.  .  . 

Loss,  400°  F.  to  constant  wt  .  . 
Penetration  of  residue 





31.0% 
13° 





Bitumen     insoluble     in    88° 
naphtha,  pitch     

9.4% 

3.5% 

40.4% 

Bitumen     insoluble    in     62° 
naphtha,  pitch 

25  9% 

Bitumen  yields  on  ignition: 
Fixed  carbon  

7  0% 

10.0% 

*  Too  large  to  read. 


130  THE  MODERN  ASPHALT  PAVEMENT. 

leums  from  California  and  the  petroleum  of  mixed  character 
from  Texas  containing  both  paraffine  and  asphaltic  hydrocarbons. 
The  residues  from  paraffine  petroleum  usually  carry  a  very  con- 
siderable amount  of  paraffine  scale,  which  has  a  decided  influence 
on  their  character.  The  residue  from  Texas  petroleum  from  the 
Beaumont  field,  now  nearly  exhausted,  contained  only  a  small 
amount  of  paraffine  hydrocarbons  and  not  more  than  1  per  cent 
of  paraffine  scale.  The  supply  of  flux  of  this  character  is  now  very 
small,  and  is  all  produced  at  Chaison,  Texas.  The  greater  part 
of  the  Texas  flux  on  the  market  in  1907  was  produced  from  pipe 
line  oil  from  the  various  Texas  and  Oklahoma  fields.  This  petro- 
leum is  necessarily  of  a  very  mixed  character  and  the  flux  pre- 
pared from  it  has  contained  very  considerable  amounts  of  paraffine 
hydrocarbons  and  scale,  the  latter  reaching  at  times  as  high 
as  six  per  cent.  It  is  far  less  satisfactory  as  an  asphaltic  flux  than 
that  prepared  from  the  original  Beaumont  oil,  and  in  some  respects 
is  not  a  suitable  substitute  for  it.  For  use  with  ordinary  asphalts 
it  is,  however,  as  good  for  paving  purposes,  although  perhaps 
not  quite  as  stable  at  high  temperatures.  It  must  be  used  as  a 
paraffine  flux.  The  California  residuum  or  flux  is  composed 
almost  entirely  of  complicated  polymethylenes  and  contains  notable 
proportions  of  aromatic  hydrocarbons,  nitrogenous  bases,  and 
phenols,  and  is  characterized  by  its  very  great  density. 

Residuums  from  the  same  kind  of  petroleum  may,  on  the 
other  hand,  vary  very  largely  among  themselves,  according  to 
the  care  with  which  they  have  been  prepared.  It  is  quite  as 
necessary,  therefore,  to  determine  whether  a  flux  has  been  care- 
fully distilled  as  it  is  to  know  the  character  of  the  petroleum  from 
which  it  has  been  produced. 

In  making  a  comparative  study  of  the  available  fluxes  it  will 
also  be  necessary  to  determine  whether  there  is  a  preference  in 
favor  of  one  over  another  as  an  actual  solvent  for  the  solid  bitu- 
mens, and  to  determine  their  stability  and  such  other  properties 
as  may  point  to  their  adaptability  for  use  in  the  preparation  of 
an  asphalt  cement. 

The  fluxes  now  in  use  in  the  paving  industry  may  be  con- 
sidered as  consisting  of  the  three  classes  which  have  been  men- 


PETROLEUMS. 


131 


tioned  above,  and  their  character  may  be  taken  up  according  to 
such  a  classification. 

Paraffine  Petroleum  Residuum. — Paraffine  petroleum  residuum 
is  the  form  of  flux  originally  used  in  the  asphalt  paving  industry 
in  the  United  States.  It  is  also  known  as  petroleum  tar  and  was 
originally  a  by-product  remaining  after  the  distillation  of  crude 
Pennsylvania  paraffine  petroleum  for  the  production  of  illumi- 
nating-oil. It  was  the  flux  used  by  De  Smedt  in  the  early  days 
of  the  paving  industry  for  imparting  a  proper  consistency  to  Trini- 
dad asphalt  in  the  production  of  paving-cement.  Its  use  has 
been  largely  continued  up  to  the  present  time,  but  its  character 
has  been  greatly  modified  and  improved.  It  is  no  longer  a  by- 
product, but  is  especially  prepared  for  the  purpose. 

In  the  early  days  of  the  industry  the  residuum  used  in  the 
preparation  of  asphalt  cement  was  of  most  varied  character. 
Among  available  records  it  is  found  that  in  the  summer  of  1888 
several  residuums  in  use  had  the  following  properties: 


Flash. 

Gravity. 

230°  F. 
203° 
226° 
392° 
428° 
176° 

22°  B. 
24° 
25° 
27° 
22° 

.9240 
.9130 
.9070 
.8950 
.9240 

The  result  of  making  a  cement  with  oil  flashing  at  176°  F. 
would  be  that  much  of  it  would  be  easily  volatilized  at  the  tem- 
perature of  melted  asphalt  cement,  325°  F.,  and  that  the  con- 
sistency would  of  course  be  most  unstable. 

In  1889  the  oils  hi  use  had  the  following  characteristics: 


Source. 

Gravity. 

Flash. 

Volatile,  400°  F. 

Eagle  Refining  Co  

22.8°  B. 

416°  F. 

14.40% 

MaToney  Oil  (To  

21.7° 

361° 

14.33 

Jenney  Mfg  Co     .  . 

20  8° 

271° 

16.80 

132  THE   MODERN   ASPHALT   PAVEMENT. 

As  late  as  1892  the  oils  were  still  variable: 


Source. 

Gravity. 

Flash. 

Volatile,  400°  F. 

Solar            .    . 

21   0°  B. 

417°  F 

4  06% 

Jenney  

18.5° 

235° 

11  20 

National  

20.0° 

295° 

15  94 

Whiting  

22.2° 

415° 

5  39 

Continental  (Denver)  

23.8° 

345° 

15  73 

Crew  Levick 

20  4° 

320° 

17  36 

In  1891  the  Standard  Oil  Company  undertook  to  prepare  a 
heavy  oil  especially  for  paving  purposes  which  should  be  fur- 
nished to  those  who  were  particular  as  to  its  character  and  were 
willing  to  pay  for  a  better  quality.  It  has  had  the  following 
average  composition  since  1896: 

PARAFFINE  RESIDUUMS.      AVERAGE  AND  EXTREMES  IN 
COMPOSITION  FOR  FOUR  YEARS. 


Year.' 

Volatile, 
400°  F. 

Extremes. 

Specific 
Gravity. 

Extremes. 

Flash. 

Extremes. 

1896 

4.7% 

2.6-  8.8 

.9313 

.9204-.  9351 

430°  F. 

397°-476° 

1897 

6.1 

1.4-12.3 

.9302 

.9219-.  9383 

420° 

393°-456° 

1898 

5.1 

2.9-  8.8 

.9327 

.9206-.  9397 

432° 

392°-455° 

1899 

3.8 

2.0-  6.4 

.9331 

.9295-.  9376 

442° 

416°-460° 

Consistency  after  heating :  Flows  slowly  at  about  78°  F. 

The  great  uniformity  of  the  supply  is  apparent.  Oil  of  the 
old  character  is  still  in  use  by  careless  contractors,  as  it  is  cheap. 
Oils  of  this  description  which  have  come  under  my  observation 
have  the  following  characteristics: 


Specific 
Gravity. 

Flash. 

Volatile, 
400°  F.,  7  Hours. 

.9100 

280°  F. 

23.9% 

.9197 

330° 

17.3 

.8829 

260° 

27.2 

.9222 

286° 

12.6 

The  best  paraffine  residuum  from  Ohio  petroleum  and  some  of 
the  Kansas  and  Colorado  fields,  which  has  been  in  use  during  the 


PETROLEUMS. 


133 


past  six  or  seven  years  has  commended  itself  in  quality  from  the 
fact  that  it  is  carefully  prepared  for  the  paving  industry  by  dis- 
tillation with  steam  agitation  without  cracking — that  is  to  say, 
decomposition  of  the  oil — that  it  has  a  high  flash  point,  and  on 
this  account  contains  little  oil  volatile  at  the  temperatures  at 
which  asphalt  cement  is  maintained  in  a  melted  condition,  and 
that  it  is  uniform.  The  possible  disadvantages  of  such  dense 
residuum,  if  they  are  such,  in  comparison  with  the  lighter  and 
more  volatile  oils  are,  that  more  of  this  oil  must  be  used  to  pro- 
duce a  cement  of  given  penetration  or  consistency  and  that  at 
comparatively  low  temperature  asphalt  cements  made  with  it 
harden  more  than  when  lighter  oils  are  used,  owing  to  the  separa- 
tion of  paraffine  scale. 

The  only  advantage  of  the  lighter  form  of  residuum,  how- 
ever, is  the  one  just  mentioned,  that  it  and  the  cement  prepared 
from  it  do  not  harden  or  solidify  as  much  in  winter  tempera- 
tures. 

Typical  Paraffine  Fluxes  of  1907. — In  the  following  table  are 
given  the  characteristics  of  various  paraffine  fluxes  which  were 
available  and  in  use  in  the  paving  industry  in  the  year  1907. 
Many  of  the  paraffine  fluxes,  analyses  of  which  were  given  in  the 
original  edition  of  this  work,  are  no  longer  available,  and  there  is 
no  assurance  that  the  supply  for  any  one  year  can  be  duplicated 
the  following  one. 


Paraffine 

Paraffine 

Paraffine 

Solar  Ref. 

S  O  Co 

S  O  Co 

Date  shipment  received  ...  

Lima,  Ohio 
10-28-07 

Whiting, 
Ind. 
10-30-07 

Neodesha, 
Kan. 
11-10-07 

100537 

100610 

100446 

gp<  gj.  —  Beaum6  —  at  78°  F  

18.4 

20  5 

21  2 

gp  gj.  —  actual  —  at  78°  F  . 

943 

930 

926 

Flash  point  degrees  F 

455 

425 

435 

Volatile  7  hours  at  212°  F.  . 

1% 

2% 

4% 

Volatile  in  7  hours,  325°  F.  (dry  sample)  .  . 
Residue  at  78°  F  

.2 
Crystalline 

1.2 
Crystalline 

.6 
Crystalline 

Bit  insol  88°  naphtha  pitch    .  .  . 

Slow  flow 
2  7 

Quick  flow 
3  4 

Quick  flow 
2  6 

Per  cent  sol.  bit.  rem.  by  H2SO4  

24  9 

24  7 

25  9 

Paraffine  scale  

6.4 

7.9 

8  9 

Fixed  carbon  

2.8 

1.9 

1.8 

134 


THE  MODERN  ASPHALT  PAVEMENT. 


The  petroleum  residuum  used  in  the  work  carried  out  under  the 
author's  supervision  is  furnished  under  the  following  specifications: 

Specifications  for  Paraffine  Flux,  1907-1908. — "This  oil  or  flux 
shall  consist  of  the  heavier  or  higher  boiling  portions  of  any  par- 
affine petroleum.  It  shall  have  a  specific  gravity  of  between  .942 
and  .924  (18.6-21.5°  B.)  at  78°  F. 

"It  shall  be  free  from  water  and  decomposition  products,  shall 
contain  not  more  -than  2%  of  bitumen  insoluble  in  88°  naphtha, 
not  more  than  10%  of  material  recovered  when  one  gram  of  the 
flux  is  treated  as  for  the  determination  of  paraffine  scale,  accord- 
ing to  the  method  described  in  "The  Modern  Asphalt  Pavement/' 
John  Wiley  &  Sons,  and  shall  not  volatilize  more  than  5%  at 
325°  F.  in  7  hours." 

It  appears  from  the  preceding  table  and  from  our  specifications 
that  a  residuum  from  a  paraffine  petroleum,  such  as  used  in  the 
asphalt  industry  at  the  present  day,  if  it  is  in  the  highest  degree 
desirable,  should  have  a  specific  gravity  of  .93,  equivalent  to  a 
density  of  21.0°  B.,  a  flash  point  of  400°  F.,  should  volatilize  but 
a  small  amount  at  325°  F.  under  certain  conditions  which  are  im- 
posed, should  be  practically  completely  soluble  in  carbon  disul- 
phide,  and  to  the  extent  of  95  per  cent  in  88°  naphtha.  The  par- 
affine scale  should  be  less  than  10  per  cent,  and  the  amount  of 
fixed  carbon  which  is  obtained  on  ignition  not  over  4  per  cent. 

It  will  be  noted  in  the  preceding  analyses  that  the  percentage 
of  paraffine  scale  varies,  in  the  samples  examined,  from  6.4  to 
8.9  per  cent.  In  other  residuums  even  more  paraffine  scale  has 
been  found,  as  can  be  seen  from  the  following  determinations 
which  were  made  some  years  ago  in  the  author's  laboratory. 


Manufacturer. 

Paraffine. 

Craig  Oil  Co  ,  Milwaukee  .          

17.6% 

Crew  Levick  Co  ,  Philadelphia  

8.7 

American  Petroleum  Product  Co.,  Find- 
lay,  Ohio  

12.3 

Scofield,  Shurmer  &  Teagle,  Indianapo- 
lis Ind                    

7  1 

Standard  Oil  Co  

14.5 

Wilburine  Oil  Co    Brooklyn  

33  3 

Standard  Oil  Co  ,  thin  oil  

9  1 

PETROLEUMS.  135 

The  smaller  the  amount  of  paraffine  scale  that  is  present  the 
more  desirable  the  flux,  since  a  substance  of  this  nature  which 
becomes  solid  at  low  temperatures  cannot  be  advantageous  in  a 
paving  cement.  That  paraffine  residuum  is  an  extremely  stable 
oil  appears  from  the  fact  that  about  75  per  cent  of  the  hydrocar- 
bons of  which  it  is  composed  are  not  attacked  in  88°  naphtha 
solution  by  concentrated  sulphuric  acid,  a  fact  which  is  confirmed 
by  exposing  such  a  residuum  to  water  for  many  years,  when  no 
action  is  found  to  have  taken  place.1 

The  characteristics  of  asphalt  cement  made  with  paraffine 
residuums  of  various  densities,  and  the  refutation  of  the  claim 
that  it  is  not  a  satisfactory  solvent  for  asphalts  and  is  unsuited 
for  the  purpose  for  which  it  is  used  hi  the  paving  industry,  will 
be  taken  up  later  when  asphalt  cements  are  under  consideration. 
It  is  merely  necessary  to  state  here  that  of  such  a  residuum  as 
has  been  described  from  18  to  22  pounds  must  be  used  with  every 
100  pounds  of  refined  Trinidad  lake  asphalt  in  order  to  produce 
a  cement  of  proper  consistency  for  paving  purposes. 

Kansas  Petroleum  Residuum. — Within  the  last  two  years 
a  flux  has  appeared  on  the  market  which  is  prepared  from  the  oils 
coming  from  the  Kansas  fields  through  pipe  lines  to  the  East. 
This  flux  is  very  peculiar  in  character.  It  possesses  largely  the 
characteristics  of  a  paraffine,  and  some  of  those  of  an  asphaltic 
flux.  It  is  peculiar  in  that,  although  it  carries  but  6.7%  of  par- 
affine scale,  it  leaves  a  solid,  cheesy  residuum  amounting  to  85% 
of  the  original  oil  on  heating  at  400°  F.,  while,  on  being  main- 
tained at  that  temperature  for  a  considerable  period  of  time,  it 
decomposes  with  the  separation  of  a  granular  insoluble  material, 
and  with  the  evolution  of  gas.  On  this  account  it  is  looked 
upon  by  the  author  as  more  or  less  unsuitable.  It  has  been  used 
to  a  very  large  extent,  however,  and  apparently  works  satis- 
factorily at  ordinary  temperatures  with  Trinidad  and  Bermudez 
asphalt.  It  is  to-day  one  of  the  largest  sources  of  supply  of  flux 

1  Whipple  &  Jackson,  The  Action  of  Water  on  Asphalt.  Engineering 
Record,  March  17,  1900,  41. 


136  THE  MODERN  ASPHALT  PAVEMENT. 

in  the  paving  industry  and  its  value  can  only  be  shown  by  service 
tests.  In  the  meantime,  it  must  be  classed  as  a  paraffine 
residuum. 

Its  characteristics  are  shown  in  the  following  table: 


Manufacturer Standard  Oil  Company, 

Brooklyn,  N.  Y. 

Received  from '. Maurer,  N.  J. 

Date  shipment  received 5-10-08 

Test  number 2857-M. 

Specific  gravity— Beaume"— at  78°  F 19.4° 

Specific  gravity — Actual — at  78°  F .937 

Flash  point,  degrees  F 485 

Volatile  in  7  hours  at  212°  F .2% 

Volatile  in  7  hours  at  325°  F.  (dry  sample) .6% 

Residue  at  78°  F Medium  slow  flow — crys- 
talline 

Volatile  in  7  hours  at  400°  F.  (dry  sample) 2.0% 

Residue  at  78°  F Medium  flow — crystalline 

Bitumen  insoluble  in  88°  naphtha,  pitch 2.7% 

Per  cent  soluble  bitumen  removed  by  H2SO4 23 . 4 

Paraffine  scale •. 2.5 

Fixed  carbon 3.5 


California  Asphaltic  Petroleum  Residuum. — The  petroleums 
of  California  are  characterized  by  the  fact  that  the  residue  left  on 
distillation,  if  the  latter  is  carried  sufficiently  far,  is  a  solid  bitu- 
men resembling  asphalt.  The  oil  is  said,  on  this  account,  to  have 
an  asphaltic  base.  If  the  distillation  is  suspended  at  a  point 
where  the  residue  does  not  solidify  on  cooling  but  remains  liquid, 
like  a  heavy  and  dense  natural  maltha,  the  material  known  as 
California  flux  is  obtained  which  has  been  in  use  in  the  paving 
industry  to  a  very  considerable  extent  on  the  Pacific  Coast  and 
to  but  a  small  extent  elsewhere.  Such  residuums,  as  found  on 
the  market  in  1907,  have  the  characteristics  given  in  the  table  on 
page  137. 

Before  discussing  the  characteristics  of  these  residuums  it  will 


PETROLEUMS. 


137 


be  necessary  to  consider  what  takes  place  in  the  process  of  their 
manufacture.  The  petroleum  is  distilled  in  cylindrical  stills  in 
the  usual  manner  with  some  steam  agitation,  the  temperature 
being  eventually  carried  up  to  about  600°  F.  or  higher,  and  main- 
tained there  until  a  sample  is  slightly  hea,vier  than  water  when 
poured  into  it.  It  is  very  evident  that  in  this  process  the  petro- 
leum is  subjected  to  a  very  severe  treatment  and  it  is  not  diffi- 
cult to  determine  at  the  plant  where  such  flux  is  produced  that 
very  decided  cracking  goes  on.  That  such  cracking  takes  place 
can  also  be  shown  by  heating  a  small  portion  of  the  original  petro- 

CALIFORNIA   ASPHALTIC   PETROLEUM   RESIDUUM. 


68489 

69607 

"No.  2" 

"G"  grade 

PHYSICAL   PROPERTIES. 

Specific  gravity,  dried  at  212°  F.,  78°  F./780  F.. 
Flashes  °  F    N  Y  State  oil-tester  . 

1.002 
354°  F. 

1.0061 
376°  F  * 

CHEMICAL   CHARACTERISTICS. 

Dry  substance  : 
Loss  325°  F  ,  7  hours  

5.9% 

3  2%  • 

Character  of  residue   

smooth 

smooth 

soft 

•oft 

Loss,  400°  F.,  7  hours  (fresh  sample)  

16.7% 

17.3% 

Character  of  residue 

smooth 

smooth 

Penetration  of  residue  at  78°  F  

soft 

soft 

Bitumen  soluble  in  CSj,  air  temperature  

99  9% 

99  7% 

Difference  

.1 

.3 

Inorganic  or  mineral  matter  

.0 

.0 

Bitumen  insoluble  in  88°  naphtha,  air  temper- 
ature, pitch      

100.0 

7.6% 

100.0 

7.7% 

Per  cent  of  soluble  bitumen  removed  by  ILjSO^  . 
Per  cent  of  total  bitumen  as  saturated  hydrocar- 
bons                                      

48.3 
47  9 

54.9 
41.9 

.0 

.0 

Fixed  carbon 

6  0 

6  0 

'Extremes  1.018-.993 


2  Extremes  430°-350°. 


3  Extremes  5.50-.83. 


leum  in  a  glass  dish  in  an  oven  at  not  over  400°  F.,  when  the  lighter 
portions  all  volatilize  without  cracking  and  the  residue  recovered 


138  THE    MODERN    ASPHALT    PAVEMENT. 

is  found  to  be  of  the  same  consistency  but  much  larger  in  amount 
than  that  obtained  by  the  industrial  process.  It  is  further  not, 
moreover,  surprising  that  cracking  should  take  place  very  readily 
with  California  petroleums,  since  it  is  known  that  they  are  com- 
posed of  the  unstable  polycyclic  polymethylenes  of  a  high  degree 
of  molecular  aggregation.1 

In  California  flux,  therefore,  we  have  one  which  is  of  a  much 
greater  density  than  that  derived  from  paraffine  petroleum,  or 
even  that  derived  from  Beaumont,  Texas,  asphaltic  oil.  It  origi- 
nates in  an  unstable  petroleum  and  has  been  subjected  to  very 
severe  treatment,  and  is,  therefore,  partially  cracked.  This  is 
apparent  in  some  of  the  determinations  given  in  the  preceding 
table,  where  the  amount  of  oils  volatile  in  seven  hours  at  400°  F. 
is  found  to  be  much  larger  than  would  be  the  case  with  a  stand- 
ard paraffine  residuum  under  similar  treatment.  This  loss,  about 
17  per  cent,  must  be  due  to  the  volatilization  of  light  oils  produced 
by  cracking. 

Of  the  components  of  these  California  fluxes  only  40  to  50  per 
cent  consist  of  saturated  hydrocarbons  as  compared  to  70  or  80  per 
cent  found  in  paraffine  residuum.  This  points  with  great  prob- 
ability to  the  conclusion  that  such  fluxes  will  harden  with  age 
and  exposure  much  more  rapidly  than  the  more  stable  paraffine 
fluxes. 

It  will  be  noted  that  the  residue  after  heating  the  California 
flux  to  400°  F.  is  still  soft.  This  is  a  property  which  is  abso- 
lutely essential  and  differentiates  these  fluxes  from  the  natural 
malthas,  which,  as  has  appeared,  usually  become  converted  into 
hard  pitches  on  heating  for  any  length  of  time  to  a  high  tem- 
perature, and  it  is  this  property  which  makes  it  possible  to  use 
the  modern  California  residuums  as  a  flux. 

The  fixed  carbon  which  the  California  residuums  yield  on 
ignition  is  larger  than  that  found  in  the  paraffine  residuum,  as 
would  be  expected  from  the  character  of  the  hydrocarbons  of 
which  it  is  composed,  those  in  the  California  oil  containing  a 

1 J.  Soc.  Chem.  Ind.,  1900,  19,  123. 


PETROLEUMS.  139 

very  considerably  larger  percentage  of  carbon  than  those  found  in 
the  eastern  residuums. 

In  drawing  specifications  for  a  California  asphaltic-  flux  it 
should  be  provided  that  it  should  remain  soft  after  heating  for 
seven  hours  at  400°  F.  The  specifications  which  the  author  has 
proposed  for  use  in  work  under  his  directions  on  the  Pacific  slope 
are  as  follows: 

Specifications  for  "  G  "  Grade  California  Flux. — "  California 
flux,  known  as  '  G  '  Grade  Flux,  should  be  a  residue  from  the 
distillation  of  California  petroleum,  with  steam  agitation,  at  a 
temperature  not  above  620°  F. 

"  It  shall  have  the  following  characteristics: 

"  It  shall  be  soluble  in  carbon  disulphide  to  the  extent  of  99 
per  cent  and  in  88°  naphtha  to  the  extent  of  90  per  cent. 

"  It  shall  be  free  from  water,  shall  not  flash  below  350°  F. 
in  a  New  York  State  oil-tester,  and  shall  have  a  density  of  not 
less  than  .98,  12.9°  B.,  or  more  than  1.050,  9.3°  B.,  at  25°  C.  when 
referred  to  water  at  the  same  temperature. 

"  It  shall  volatilize  not  more  than  5  per  cent  of  oil  when  heated 
for  seven  hours  at  325°  F.,  according  to  the  method  employed  in 
the  New  York  Testing  Laboratory. 

"  The  residue  from  heating  the  oil  in  the  same  way  to  400°  F. 
for  seven  hours  shall  be  a  soft  flux  not  hard  enough  to  give  a  pen- 
etration of  less  than  150°  with  the  Bowen  penetration  machine. 

"  It  shall  not  yield  more  than  6  per  cent  of  fixed  carbon  on  igni- 
tion. Under  the  microscope,  beneath  a  cover-glass,  it  shall  appear 
free  from  insoluble  or  suspended  matter." 

One  of  the  most  important  characteristics  of  a  California  flux 
to  be  noted  from  an  industrial  point  of  view  is  that,  owing  to 
its  great  density,  more  than  twice  as  much  of  it  is  required  to 
soften  the  solid  native  bitumens  as  of  a  paraffme  residuum 
or  of  one  of  the  semi-asphaltic  nature  produced  from  Texas  oil. 
For  example,  with  Trinidad  asphalt  51  pounds  of  a  California 
flux  are  often  necessary  to  make  a  cement  of  normal  penetration 
where  no  more  than  22  pounds  of  paraffine  residuum  are  used. 

The  disadvantages  to  be  met  with  in  the  use  of  a  California 
flux  or  the  defects  in  its  character  have  been  presented  in  the 


140  THE  MODERN  ASPHALT  PAVEMENT. 

preceding  paragraphs.  Aside  from  this  the  flux  presents  certain 
advantages  and  desirable  properties  which  cannot  be  equalled 
in  any  other  softening  agent,  and  on  this  account  makes  it  of 
great  value  in  certain  problems  in  the  paving  industry.  With 
an  asphalt  such  as  that  from  La  Patera,  California,  or  the  Bejucal 
mine  in  Cuba,  a  satisfactory  paving  material  could  not  be  made 
were  it  not  possible  to  supply  the  deficiencies  of  malthenes  in 
these  hard  bitumens  by  means  of  those  present  in  a  California 
flux.  The  use  of  the  material  in  this  way  was  well  illustrated 
in  the  Alcatraz  XX  asphalt,  which  was  formerly  on  the  market. 
Sixty  per  cent  of  La  Patera  asphalt  was  mixed  with  40  per  cent  of 
dense  California  residuum  and  the  resulting  product  was  a  bitumen 
which  contained  asphaltenes  and  malthenes  in  normal  propor- 
tions, and  which,  when  made  with  care  and  uniformity,  proved  a 
desirable  material.  Great  uniformity  in  its  manufacture  was  not 
possible,  however,  and  the  defects  inherent  therein  will  be  consid- 
ered when  the  study  of  asphalt  cements  is  taken  up. 

As  in  the  case  of  paraffine  residuums,  so  with  the  California 
fluxes :  in  the  early  days  of  the  industry  they  were  not  at  all  care- 
fully prepared,  and  even  to-day  many  of  them  are  found  on  the 
market  which  are  too  badly  cracked  to  be  desirable.  They  can, 
with  care,  however,  be  prepared  with  a  very  considerable  degree 
of  uniformity,  as  can  be  seen  from  the  extremes  given  in  the  table 
on  page  137. 

As  an  example  of  an  unsatisfactory  flux  the  following  will 
serve: 

TEST  NO.  69012. 

Specific  gravity,  78°  F./780  F 9815 

Loss,  212°  F 8% 

"      325°  F.,  7  hours 8.0 

"      400°  F.  "     "    (fresh  sample) 16.2 

Penetration  of  400°  F.  residue 43° 

Bitumen  insoluble  in  88°  naphtha,  air  temp.     9.0% 
Fixed  carbon 6.0 

In  this  flux  the  specific  gravity  is  low,  with  the  result  that 
there  is  a  large  loss  of  volatile  matter  at  325°  F.,  while  the  residue 
after  heating  to  400°  F.  is  a  solid  bitumen,  showing  that  the  flux 
is  not  a  stable  one  and  therefore  undesirable. 


PETROLEUMS. 


141 


Fluxes  from  Beaumont  and  Similar  Oils. — Petroleum  of  the 
character  of  that  found  in  the  well-known  Beaumont  field  in 
Texas  is  usually  considered  to  have  an  asphaltic  base,  but,  as  is 
not  so  well  known,  it  also  contains  a  very  considerable  propor- 
tion of  paraffine  hydrocarbons,  or  hydrocarbons  which  are  ex- 
tremely stable,  as  shown  by  then*  behavior  with  sulphuric  acid,1 
the  loss  on  treatment  of  the  crude  oil  with  sulphuric  acid  being 
only  39  per  cent  as  compared  with  30  per  cent  for  an  Ohio  oil 
and  a  still  larger  amount  for  the  asphaltic  petroleums  of  Cali- 
fornia. The  result  is  that  the  residuum  or  flux  prepared  from 
Beaumont  petroleum  possesses  some  very  desirable  properties,  as 
revealed  by  the  following  determinations: 

BEAUMONT,  TEXAS,  FLUX. 


69330 

66364 

Oualitv 

light 

heavy 

PHYSICAL   PROPERTIES. 

Specific  gravity,  dried  at  212°  F.,  78°  F./780  F.  . 
Flashes  °  F    N  Y  State  oil-tester         

.9565 
395°  F 

.9735 
418°  F. 

CHEMICAL   CHARACTERISTICS. 

Dry  substance  : 
Loss  325°  F    7  hours  

4.3% 

•  8% 

smooth 

smooth 

Penetration  of  residue  at  78°  F  

soft 

soft 

Loss  400°  F    7  hours  (fresh  sample)  

14.5% 

6.2% 

Character  of  residue                

smooth 

smooth 

soft 

soft 

Bitumen  soluble  in  CS    air  temperature    

99.8% 

99.6% 

Difference                                  .        

.2 

.4 

.0 

.0 

Bitumen  insoluble  in  88°  naphtha,  air  temper- 
ature, pitch 

100.0 
2.5% 

100.0 

4.8% 

Per  cent  of  soluble  bitumen  removed  by  H.jSO4.  . 
Per  cent  of  total  bitumen  as  saturated  hydrocar- 
bons    

25.4 
72.8 

20.9 
79.4 

1.0 

1.7 

3.0 

3.5 

1 J.  Soc.  Chem.  Ind.,  1901,  20,  690. 


142  THE  MODERN  ASPHALT  PAVEMENT. 

When  the  preceding  results  are  compared  with  those  which 
have  been  given  as  representing  the  character  of  the  paraffine 
residuums  and  of  California  fluxes,  it  will  be  seen  that  the  density 
of  these  oils  is  much  higher  than  that  of  the  true  paraffine  residuums, 
but  much  lower  than  that  of  the  California  fluxes,  and  that  the 
percentage  of  total  bitumen  which  is  present  as  saturated  hydro- 
carbons is  between  70  and  80  per  cent  as  compared  to  40  and 
50  per  cent  in  the  latter  form  of  flux.  This  must  be  a  very  desir- 
able property  and  one  which  is  due  probably  to  the  presence 
of  an  appreciable  amount  of  paraffine  hydrocarbons  and  of  a 
large  proportion  of  stable  polymethylenes.  The  investigations 
of  Mabery  and  the  author  have  shown  that  the  polymethylenes 
belong  to  the  CnH2n,  CnH2n-2,  and  CnH2n_4  series.  That  par- 
affine hydrocarbons  are  present,  and  that  some  of  them  are  of 
high  molecular  weight,  is  revealed  by  the  fact  that  the  residuum 
contains  1  per  cent  of  paraffine  scale.  As  prepared  for  use  as  a 
flux  the  residuum  is  much  denser  than  ordinary  paraffine  flux, 
its  specific  gravity  being  .95  to  .96  as  compared  with  .93  for  the 
latter.  In  other  respects,  when  very  carefully  prepared,  it  is  not 
essentially  different  in  its  physical  properties.  It  sometimes  con- 
tains a  slightly  larger  proportion  of  light  oils,  volatile  at  325°  F., 
but  the  same  proportions  of  the  lighter  flux  and  hard  asphalt 
are  necessary  as  in  the  case  of  paraffine  residuum.  The  denser 
form,  with  a  gravity  of  .97,  is  only  used  with  asphalts  that  are 
deficient  in  malthenes,  such  as  Trinidad  land  asphalt. 

The  above  conclusions  only  hold  true  when  the  residuum  is 
carefully  prepared  and  some  is  found  on  the  market  which, 
like  the  less  carefully  distilled  paraffine  residuum  of  the  earlier 
years  of  the  industry,  is  not  satisfactory.  If  carefully  prepared, 
however,  it  is  without  doubt  the  most  desirable  flux  which  is 
available  to-day  for  the  purpose  for  which  it  is  used. 

Specifications  for  this  residuum  may  read  as  follows: 

"This  oil  or  flux  shall  consist  of  the  heavier  or  higher  boil- 
ing hydrocarbons  of  Texas  oil  containing  not  more  than  3  per 
cent  of  paraffine  scale,  as  determined  according  to  the  method 
described  in  "The  Modern  Asphalt  Pavement,"  John  Wiley 
&  -Sons.  It  shall  be  of  a  character  suitable  for  fluxing 


PETROLEUMS.  143 

grahamite  and  other  hard  bitumens  in  such  a  way  that,  when 
forty  (40)  parts  of  grahamite  and  sixty  (60)  parts  of  the  flux  are 
melted  together  at  400°  F.,  the  resulting  product  shall  not,  after 
24  hours  in  an  ice  box,  contain  free  oil  or  have  a  granular  or  short 
structure,  due  to  the  presence  of  paraffine.  It  shall  have  a  gravity 
not  less  than  .97  at  78°  F.,  shall  not  volatilize  more  than  five  per 
cent  when  heated  at  400°  F.  for  seven  (7)  hours,  and  shall  not 
flash  below  400°  F.  in  a  closed  oil  tester,  New  York  State  pattern. 

"It  shall  be  free  from  water  and  decomposition  products,  con- 
tain not  more  than  3%  of  bitumen  insoluble  in  88°  naphtha, 
and  shall  not  volatilize  more  than  5  per  cent  when  heated  for 
seven  (7)  hours  at  a  temperature  of  325°  F." 

As  has  already  been  said,  the  supply  of  flux  of  this  description 
is  nearly  exhausted  at  the  present  time,  owing  to  the  decline  of 
the  Beaumont  field  and  the  mixing  of  petroleums  from  various 
fields  in  pipe  lines,  many  of  which  contain  a  large  proportion  of 
paraffine  oil. 

Other  Fluxes. — While  the  fluxes  which  have  been  previously 
described  are  those  which  are  actually  hi  use  hi  the  industry  in 
the  United  States,  others  are  found  on  the  Continent  of  Europe 
which,  although  not  available  for  use  in  this  country,  would  be 
entirely  satisfactory  if  this  were  the  case.  Among  these  may 
be  mentioned  residuum  from  the  distillation  of  Russian  petroleum. 
This  is  free  from  paraffine  scale  and  consists  of  very  stable  hydro- 
carbons, and  with  it  an  especially  desirable  asphalt  cement  could 
be  made,  if  it  were  reduced  to  a  proper  density  and  uniformity. 

In  France  residuum  from  the  distillation  of  shale  oils  is  avail- 
able and  is  largely  used  in  the  fluxing  of  asphalts  for  use  hi  mastic. 
Such  an  oil  has  the  properties  shown  in  table  on  page  144. 

It  will  be  noticed  that  this  oil  consists  very  largely  of  unstable 
hydrocarbons,  as  would  be  expected  in  one  which  is  the  product 
of  the  distillation  of  shales,  a  process  in  which  cracking  must  go 
on  to  a  certain  extent,  and  contains  a  very  considerable  quantity 
of  paraffine  scale. 

Wax  Tailings. — Wax  tailings,  or  still  wax,  is  a  thick,  yellow- 
brown  buttery  product  at  ordinary  temperature,  which  melts 
to  a  thin  liquid  at  about  175°  F.  It  is  the  product  of  the  destruc- 


144 


THE  MODERN  ASPHALT   PAVEMENT. 


SHALE-OIL    RESIDUUM    FROM    FRANCE.      GOUDRON    DE 
SCHISTE  D'AUTUN. 


65402 

72630 

PHYSICAL   PROPERTIES 

Specific  gravity,  dried  at  212°  F.,  78°  F./780  F.  . 
Flashes  °  F    N   Y  State  oil-tester       

.9849 
215°  F 

.9894 
355°  F. 

CHEMICAL   CHARACTERISTICS. 

Dry  substance  : 
Loss,  325°  F  ,  7  hours  

7.6% 

5.0% 

Character  of  residue                                      .  . 

«/ 

soft 

*/ 

soft 

Loss  400°  F    7  hours  (fresh  sample)  

26.4% 

10.0% 

Character  of  residue       

soft 

soft 

Bitumen  soluble  in  CS    air  temperature 

99  7% 

99  8% 

Difference 

3 

2 

Inorganic  or  mineral  matter                              . 

o 

trace 

Bitumen  insoluble  in  88°  naphtha,  air  temper- 
ature pitch 

100.0 

6  4% 

100.0 

7  3% 

Per  cent  of  soluble  bitumen  removed  by  H2SO4.  . 
Per  cent  of  total  bitumen  as  saturated  hydro- 
carbons          

53.5 
43.6 

56.2 
43.5 

Per  cent  of  solid  paraffine             

4  4 

5  2 

Fixed  carbon   

3.0 

5.0 

live  distillation  of  paraffine  petroleum  residuum,  the  residue  in 
the  still  being  coked. 

Owing  to  the  method  of  preparation  the  product  found  on 
the  market  is  extremely  variable  in  character.  The  results  of  the 
examination  of  several  lots  in  the  author's  laboratory  are  given 
in  the  table  on  p.  145. 

It  appears  from  the  data  given  that,  as  has  been  said, 
wax  tailings  are  extremely  variable  in  character.  They  often 
carry  a  large  amount  of  water  and  vary  in  specific  gravity  and 
flash  point.  Usually  they  contain  but  little  volatile  oil,  although 
on  heating  at  400°  F.  they  become  converted,  as  a  rule,  into  a 
solid  substance  of  various  degrees  of  consistency.  Wax  tailings 
are  almost  absolutely  pure  bitumen,  and  it  is  surprising  to  find 
that,  although  they  are  the  result  of  destructive  distillation,  they 


PETROLEUMS. 
WAX  TAILINGS. 


145 


Test  number       .       

30245 

55285 

64439 

64587 

64916 

Original  material: 
Loss,  212°  F.,  until  dry.  . 
*  '      325°  F  ,  7  hours.  .  . 

7.0% 

le  2%i 

2.8%l 

15.5%' 

Residue—  pen.  at  78°  F  .  . 

Dry  material: 
Specific    gravity    78°  F./ 
78°  F       

1  02 

58° 
1  0794 

1  1445 

1  0994 

Flashes,  °  F      

298°  F. 

240°  F. 

340°  F 

410°  F 

Loss,  325°  F.,  7  hours  
Residue  —  pen  at  78°  F.  .  . 

5.9% 
83° 



3.0% 
58° 

2.1% 
soft 

Loss,  400°  F.  ,  7  hours  (fresh 
.sample).  
"-Residue.  —  pen.  at  78°  F. 

13.3% 
brittle 





4.8% 
9° 

4-6% 
50° 

B;aimen  soluble  in  CS,.  .-.  .  . 
^iflference  

99.  9%2 





99.8% 
2 

99.8% 
2 

ID  organic  or  mineral  matter. 

0 

o 

Bitumen  sol.  in  88°  naphtha 

83  1% 

97  2% 

100.0 
96  7% 

100.0 
98  1<& 

This  is  per  cent  of  total  bitu- 
men   

96  9 

98  4 

Bitumen  sol  in  62°  naphtha 

98  9% 

99  6% 

This  is  per  cent  of  total  bitu- 
men   

99  1 

99  7 

88°  naphtha  sol.  bitumen  : 
Per  cent  not  removed  by 
H2SO4  . 

49  3% 

50  0% 

55  0% 

Unacted  on  by  H^O^SOa.  .  . 
Paraffine  scale  

3.7% 



0.4 

1.1 

2.3 

Fixed  carbon  

5.5 

4  1 

3  4 

Bitumen   insoluble  in   cold 
carbon  tetrachloride  

0.0 

0  0 

Contains  a  large  amount  of  wat«r. 


2  Unacted  on  by  HaSO,,  79.9%. 


contain  50  per  cent  of  saturated  hydrocarbons  unacted  upon  by 
strong  sulphuric  acid,  although  fuming  sulphuric  acid  destroys 
them  entirely.  Although  produced  from  a  residuum  carrying 
considerable  paraffine  scale,  mere  traces  of  this  material  are  found 
in  the  tailings.  The  amount  of  fixed  carbon  which  they  yield 


146  THE    MODERN    ASPHALT   PAVEMENT. 

is  low,  as  would  be  expected  in  the  case  of  a  substance  derived 
from  paraffine  petroleum.  Wax  tailings,  owing  to  the  lack  of 
uniformity  in  the  material,  are  of  no  interest  in  the  paving  indus- 
try, but  are  used  to  a  very  considerable  extent  in  insulating  and 
other  bituminous  compounds. 

SUMMARY. 

From  the  preceding  data  it  appears  that  there  are  three 
classes  of  fluxes  available  commercially  in  the  United  States  for 
the  softening  of  native  solid  bitumens  in  the  preparation  of 
asphalt  cement  for  paving  purposes:  paraffine  residuums,  as- 
phaltic  residuums  of  California,  and  the  semi-asphaltic  residuums 
of  Texas,  and  from  the  Oklahoma  and  Kansas  fields,  the  Texas 
being  the  most  desirable  of  all  and  probably  sufficiently  superior 
to  the  good  paraffine  residuums  to  justify  an  additional  expendi- 
ture for  its  use  in  work  of  the  highest  grade,  the  reasons  for  which 
have  appeared  in  the  preceding  pages. 

The  standard  residuums  from  paraffine  oil  will,  however,  con- 
tinue to  be  used  over  a  large  area  of  country  where  they  can  be 
obtained  at  considerably  lower  prices  than  other  fluxes  and  where 
the  conditions  to  be  met  are  such  that  they  are  entirely  satisfac- 
tory. 


CHAPTER  IX. 
THE  SOLID  BITUMENS. 

WITH  the  solid  bitumens,  consisting  largely  of  paraffine  hydro- 
carbons, such  as  ozocerite,  hatchettite,  etc.,  the  paving  industry 
has  nothing  to  do,  nor  is  it  interested  in  the  terpenes,  fossil  resins, 
amber,  etc.,  which  are  composed  largely  of  unsaturated  cyclic 
compounds.  Our  attention  must  be  at  once  turned,  therefore, 
to  the  solid  bitumens  which  are  of  commercial  importance  in  the 
paving  industry,  especially  the  asphalts. 

The  Asphalts. — The  asphalts  industrially  include  all  the  solid 
native  bitumens  which  are  in  use  in  the  paving  and  other  industries. 
Specifically,  true  asphalt  is  sharply  differentiated  from  several  of 
the  bitumens  which  are  used  under  this  designation,  such  as 
gilsonite  and  grahamite.  In  the  table  which  follows  the  physical 
properties  and  proximate  composition  of  the  more  prominent 
asphalts,  using  the  term  in  its  industrial  sense,  which  are  or  have 
been  used  in  the  paving  industry,  are  given. 

Until  recently  but  little  has  been  known  of  the  nature  of 
asphalt  beyond  the  fact  that  it  is  a  native  bitumen.  Boussingault's 
investigation  of  the  viscid  bitumen  and  asphalt  of  Pechelbron,  so 
often  quoted,  threw  no  light  on  the  question  from  the  point  of  view 
of  modern  chemistry,  as  he  merely  separated  the  material  into  two 
portions,  one  more  volatile  than  the  other,  and  both,  without 
doubt,  more  or  less  decomposed  by  the  heat  to  which  they  were 
subjected,  and  consisting  of  mixtures  of  various  hydrocarbons  and 
their  derivatives.  Warren,  who  revised  the  subject  of  the  hydro- 
carbons for  Dana's  Mineralogy,  states  that  the  following  "  classes 
of  ingredients  "  are  present  in  asphalt  (see  page  150) : 

147 


148 


THE  MODERN  ASPHALT  PAVEMENT. 


PHYSICAL  PROPERTIES  AND  PROXIMATE 


Test  number                

63260 

36721 

liituinen                     

Trinidad  lake 

Trinidad  land 

PHYSICAL    PROPERTIES. 

Specific  gravity,  78°  F./780  F.      Original  sub- 
stance, dry            .        

refined. 
1  40 

refined. 
1  4196 

Blue  black 

Brown  black 

Lustre       

Dull 

Dull 

Structure  ;  

Homogeneous 

Homogeneous 

Fracture                                      

Semi- 

Semi- 

Hardness  original  substance     

conchoidal 
2 

conchoidal 
2 

Odor           

Asphaltic 

Asphaltic 

Softens  

180°  F. 

188°  F 

Flows 

190°  F 

198°  F 

Penetration  at  78°  F 

7° 

0° 

CHEMICAL   CHARACTERISTICS. 

Dry  substance: 
Loss,  325°  F  ,  7  hours  

1  1% 

1  0% 

Character  of  residue  

Smooth 

Blistered 

Loss  400°  F    7  hours  (fresh  sample)  . 

4  0% 

3  0% 

Character  of  residue  .              

Blistered 

Blistered 

Bitumen  soluble  in  CS2,  air  temperature  

56  53% 

54  1% 

Inorganic  or  mineral  matter  

36  50 

38  0 

Difference  .  .        ... 

6  97 

7  9 

Malthenes  : 
Bitumen  soluble  in  88°  naphtha,  air  tem- 
perature   

100.0 
35  6% 

100.0 
33  5% 

This  is  per  cent  of  total  bitumen  
Per  cent  of  soluble   bitumen   removed  by 
H2SO4        .                               

63.1 
61  3 

61.9 
64  8 

Per  cent  of  total  bitumen  as  saturated  hy- 
drocarbons   

24  4 

21  8 

Bitumen  soluble  in  62°  naphtha  

41.7% 

38  2% 

This  is  per  cent  of  total  bitumen  

73.9 

70.6 

Carbenes: 
Bitumen   insoluble  in  carbon  tetrachloride, 
air  temperature  

0  0% 

Bitumen    more   soluble   in    carbon    tetra- 
chloride, air  temperature 

1  3% 

Bitumen  yields  on  ignition: 
Fixed  carbon  

108% 

12.9% 

Sulphur  

0.2% 

5.0% 

1  These  bitumens  are  not  strictly  asphalts,  as  appears  in  the  text,  but  may 


THE  SOLID   BITUMENS. 
COMPOSITION  OF  THE  MORE  IMPORTANT  ASPHALTS. 


149 


44412 
Bermudez 
refined,  1900 

67753 
Bermudez 
refined,  1903 

22220 
Cuban, 
Bejucal.1 

13541 

Califorina, 
La  Patera. 

13601 
California, 
Standard.1 

66923 
Mara- 
caibo. 

1.0823 
Black 
Bright 
Uniform 
Semi- 
conchoidal 
Soft 
Asphaltic 
170°  F 
180°  F. 
22° 

1.0575 
Black 
Bright 
Uniform 
Semi- 
conchoidal 
Soft 
Asphaltic 
160°  F. 
170°  F. 
26° 

1.305 
Red-brown 
Dull 
Compact 
Semi- 
conchoidal 
2 
Asphaltic 
230°  F. 
240°  F. 
0° 

1.3808 
Black 
Dull 
Uniform 
Irregular 

2 

Asphaltic 
260°  F. 
300°  F. 
0° 

1.0627 
Black 
Dull 
Uniform 
Semi- 
conchoidal 
Soft 
Asphaltic 
170°  F. 
180°  F. 
0°-27° 

1.0638 
Black 
Bright 
Uniform 
Semi- 
conchoidal 
Soft 
Asphaltic 
200°  F. 
210°  F. 
20° 

3.0% 
Smooth 

4.4% 
Smooth 

.88% 
Cracked 

1-5% 
Shrunken 

6.6% 
Smooth 

2,7% 
Blistered 

8.2% 
Wrinkled 

9-5% 
Shrunken 

1-5% 
Wrinkled 

2.5% 
Shrunken 

19.9% 
Blistered 

4.7% 
Much  blist. 

95.0% 
2.5 
2.5 

96.0% 
2.0 
2.0 

75.1% 
21.4 
3.5 

49.3% 
48.6 
2.1 

89.8% 
6.8 
3.4 

96.8% 
1.8 
1.4 

100.0 

100.0 

100.0 

100.0 

100.0 

100.0 

62.2% 
65.4 

69.1% 
71.9 

32.4% 
43.1 

21.6% 
43.8 

53.4% 
59.4 

45.7% 
47.2 

62.4 

67.3 

60.5 

81.4 

51.9 

46.4 

24.4 

23.4 

17.0 

8.1 

28.6 

25.3 

69.2% 

72.8 

0.1% 

75.9% 
79.0 

1.1% 

39.6% 
52.7 

%:l% 

60.0% 
66.8 

0.3% 

51.5% 
53.2 

17  5% 

1  6% 

1  7% 

13.4% 
4.0% 

14.0% 

25.0% 

8-3% 

14.9% 
6.2% 

8.0% 

18.0% 

be  considered  as  such  in  their  relation  to  the  asphalt  paving  industry. 


150  THE  MODERN  ASPHALT  PAVEMENT. 

WARREN'S  CHARACTERIZATION  OF  ASPHALTUM.* 

"A.  Oils  vaporizable  at  or  about  100°  or  below;  sparingly 
present  if  at  all. 

"B.  Heavy  oils,  probably  of  the  Pittoliumor  Petrolene  groups; 
vaporizable  between  100°  and  250°,  constituting  some- 
times 85  per  cent  of  the  mass. 

"C.  Resins  soluble  in  alcohol. 

"D.  Solid  asphalt-like  substance  or  substances,  soluble  in  ether 
and  not  in  alcohol;  black,  pitch-like,  lustrous  in  fracture; 
15  to  85  per  cent. 

"E.  Black  or  brownish  substance  or  substances,  not  soluble  in 
either  alcohol  or  ether;  similar  to  D  in  color  and  appear- 
ance (Kersten);  brown  and  ulmin-like  (Volckel);  1  to 
75  per  cent. 

"F.  Nitrogenous  substances;  often  as  much  as  corresponds  to 
1  or  2  per  cent  of  nitrogen." 

He  also  defines  asphalt  as  "  a  mixture  of  different  hydrocar- 
bons parts  of  which  are  oxygenated." 

In  the  light  of  our  present  information  neither  the  classifica- 
tion of  the  proximate  constituents  nor  the  definition  of  asphalt 
is  satisfactory. 

A.  Hard  asphalts  and  but  few  malthas  seldom  contain  any 
oils  vaporizable  at  100°.     Such  hydrocarbons  cannot  be  present 
in  any  amount  in  a  hard  asphalt,  as  the  material  would  then  have 
the  properties  of  a  maltha. 

B.  Heavy   oils    are    undoubtedly   the    chief   constituents   of 
asphalt  and  as  such  require  the  most  careful  study  and  differ- 
entiation to  determine  their  nature.     Recent  investigations  have 
shown  that  these  oils  are  a  mixture  of  saturated  and  unsaturated 
hydrocarbons    of  di-  and  polycyclic  series   and  of  their  sulphur 
and  nitrogen  derivatives,  the  sulphur  derivatives  being  particu- 
larly characteristic  of  asphalt.     This  class  of  oils  is  that  which 
we  name  to-day  malthenes. 

C.  Resins  are  not  present  in  asphalt.    The  oils  are  slightly 
soluble  in  alcohol,  but  the  soluble  portion  is  not  similar  to  resin 
in  its  behavior  towards  reagents. 

1  Descriptive  Mineralogy,  Dana,  £th  Edition,  1896,  1017. 


THE  SOLID  BITUMENS.  151 

D.  The  substances  soluble  in  ether  are  soft  and  resemble  mal- 
thas.    They  are  the  same  substances  mentioned  under  B.     They 
usually  amount  to  from  60  to  75  per  cent  of  the  asphalt. 

E.  The  bitumen   not  soluble  in  ether  (petroleum  naphtha  is 
now  commonly  used  instead  of  ether  as  a  solvent)  is  a  hard  sub- 
stance which  does  not  melt  without  decomposition  but  is  soluble 
in  the  malthenes,   the  predominating  constituent  of  asphalt,    or 
in  heavy  asphaltic   oils.     Together  with   the  malthenes  it   con- 
stitutes  the   pure  bitumen   of  asphalts.     It   contains   the  larger 
part  of  the  sulphur  compounds  present  and  seems  to  owe  its  hard- 
ness to  this  fact.     It  is  known  as  asphaltenes. 

F.  Nitrogenous  substances    are    found  both  in  the  malthenes 
and  in  the  hard  bitumens  of  class  E.     In  the  malthenes  the  nitro- 
gen derivatives  have  been  identified  as  hydrocyclic  bases. 

As  has  already  been  said,  there  is  a  decided  difference  in  the 
use  of  the  term  asphalt  in  an  industrial  and  specific  sense. 

From  investigations  carried  on  in  the  author's  laboratory 
within  the  last  seven  years,  the  results  of  which  have  been  largely 
published  elsewhere,1  it  is  possible  to  characterize  true  asphalt  more 
closely  and  to  differentiate  it  specifically  from  other  solid  bitumens. 

Asphalt  may  be  defined,  industrially,  as  a  mineral  pitch, 
found  in  nature  in  a  more  or  less  solid  state,  melting  at  a  tempera- 
ture in  the  neighborhood  of  that  of  boiling  water,  and  miscible  in  all 
proportions  with  heavy  petroleum  oils  or  fluxes  to  form  a  viscous 
cementing  material  which  is  in  use  in  the  paving  and  in  other 
industries. 

More  specifically  asphalt  is  a  bitumen  found  in  nature,  orig- 
inating in  certain  types  of  petroleum,  of  various  degrees  of 
consistency,  but  generally  solid,  softening  at  a  temperature  in 
the  neighborhood  of  100  degrees  Centigrade,  and  consisting  of  a 
mixture  of  various  saturated  and  unsaturated  hydrocarbons  and 
their  derivatives,  a  part  of  which  are  soluble  in  naphtha,  very 
viscous  liquids,  largely  saturated  hydrocarbons  unattacked  by 
strong  sulphuric  acid  in  such  a  solvent;  while  those  insoluble  in 
naphtha  are  soluble  in  carbon  disulphide  and  carbon  tetrachloride, 

1  On  the  Nature  and  Origin  of  Asphalt,  Long  Island  City,  N.  Y.,  1898. 


152  THE  MODERN  ASPHALT  PAVEMENT. 

brittle  solids  which  do  not  melt  by  themselves  without  decom- 
position on  the  application  of  heat. 

The  naphtha  soluble  bitumen  is  known,  conventionally,  as  a 
class,  as  "Malthenes,"  while  the  bitumen  insoluble  in  naphtha,  but 
soluble  in  carbon  disulphide,  has  been  called  "Asphaltenes."  The 
malthenes  consist  in  part,  depending  upon  the  hardness  of  the  bitu- 
men, of  from  20  to  50  per  cent  of  saturated  di-  or  polycyclic  poly- 
rnethylenes  of  the  series  of  CnH2n_2;  CnH2n_4,  CnH2n_8,  etc.,  the 
lowest  member  found  in  Trinidad  asphalt  being  C^H^  boiling  at 
165°  C.  under  a  pressure  of  30  mm.;  in  part  of  unsaturated  hydro- 
carbons, which  can  be  separated  from  the  polymethylenes  by 
strong  sulphuric  acid  with  which  they  combine  readily,  the  nature 
of  which  is  not  so  well  understood;  of  sulphur  compounds  separated 
in  the  same  way  which,  on  isolation,  are  found  to  be  the  same  as 
those  occurring  in  Ohio,  Canadian,  and  California  petroleum  and 
nitrogen  derivatives,  perhaps  bearing  the  same  relation  to  the  poly- 
methylenes that  chinolin  does  to  benzol.  The  structure  of  these  sat- 
urated hydrocarbons  is  given  on  page  105.  The  asphaltenes 
are  probably  unsaturated  hydrocarbons  or  their  derivatives,  as 
they  are  all  strongly  acted  upon  by  concentrated  sulphuric  acid. 
The  molecules  of  which  they  consist  must  be  highly  condensed  and 
have  a  very  high  molecular  weight.  Of  their  structure  we  know 
nothing.  The  asphaltenes  contain  the  greater  part  of  the  sul- 
phur present  in  asphalts,  and  they  are,  as  a  rule,  characterized 
by  the  presence  of  very  considerable  amounts  of  it,  the  larger 
the  amount  the  harder  the  asphalt.1  Normal  asphalts  yield  about 
from  10  to  15  per  cent  of  fixed  carbon  on  ignition,  a  fact  which 
enables  us  to  differentiate  them  by  this  characteristic  alone  from 
many  of  the  other  solid  bitumens. 

Differentiation  of  the  Asphalts  among  Themselves. — Considered 
as  pure  bitumens,  the  asphalts  vary  quite  largely  in  character  among 
themselves,  depending  upon  the  nature  of  the  bitumen  from  which 
they  have  been  derived,  the  extent  to  which  they  have  been  met- 
amorphosed by  their  environment,  and  the  resulting  difference 
in  the  relative  proportions  of  malthenes  and  asphaltenes,  and 

1  On  the  Nature  and  Origin  of  Asphalt,  Long  Island  City,  N.  Y.,  1898. 


THE    SOLID    BITUMENS.  153 

of  saturated  and  unsaturated  hydrocarbons  which  are  present. 
Those  asphalts  which  have  undergone  the  most  complete  meta- 
morphism  contain  the  largest  portion  of  the  asphaltenes  and  are 
the  harder.  A  high  percentage  of  sulphur  also  works  in  the  same 
direction.  Some  actual  variations  in  the  amount  of  the  total 
bitumen  soluble  in  cold  88°  naphtha  in  asphalts  of  different  degrees 
of  hardness  are  as  follows: 

No.  22220.  Hard  asphalt,  Bejucal,  Cuba 43.1% 

"    13541.      "          "        La  Patera,  Cal 43.8 

Medium  hard,  Trinidad 65.0 

Softer  asphalt,  Bermudez 69:0 

The  following  differences  have  been  noted  in  the  amount  of 
sulphur  found  in  the  pure  bitumen  from  the  same  localities: 

No.  13541.  La  Patera,  Cal. . 6.20% 

"    22220.  Cuban,  Bejucal 8.28 

"    63260.  Trinidad  Lake 6.16 

"    44412.  Venezuela,  Bermudez 3 .93 

The  asphalts  can  also  be  differentiated  by  their  physical  prop- 
erties, such  as  consistency,  which  is  particularly  valuable,  by 
their  melting-point,  color,  and  specific  gravity,  though  in  the  form 
of  pure  bitumen  they  are  not  very  variable  in  the  latter  respect, 
and  by  other  minor  differences. 

Asphalt  Associated  with  Mineral  Matter. — In  the  preceding 
paragraphs,  asphalt  has  been  considered  as  a  more  or  less  pure 
bitumen,  but  it  is  more  often  than  not  associated  with  mineral 
matter  of  one  kind  or  another.  This  fact  has  resulted  in  a  classi- 
fication of  this  material  on  this  ground  alone,  according  to  the 
nature  of  the  mineral  matter.  Such  a  classification  may  be  of 
some  industrial  value,  although  having  nothing  to  do  with  the 
character  of  the  asphalt  itself.  At  best  it  is  artificial.  The  fol- 
lowing, based  on  the  writer's  investigation  of  a  large  number  of 
asphalts  from  all  over  the  world,  is  suggested: 

Asphalt. — 1.  Impregnating  compact,  amorphous  limestones 
to  the  extent  of  less  than  16  per  cent. 

2.  Impregnating  limestones,  partially  crystalline  and  mixed 
with  silica  or  silicates,  to  the  same  extent. 


154  THE  MODERN  ASPHALT  PAVEMENT. 

3.  Impregnating  fossiliferous  limestones  to  the  same  extent. 

4.  Impregnating  shales  or  schists. 

5.  Impregnating  hard  sandstones. 

6.  Mixed  with  silica  and  clay  to  a  fixed  and  uniform  extent 
at  the  source  where  the  asphalt  originates. 

7.  Mixed  with  sands  by  percolation  into  beds  of  the  latter  in 
place. 

8.  Mixed  with  soil  and  organic   matter  of  vegetable  origin 
where  the  effusion  of  tar  springs  have  hardened  on  exposure. 

Type  1  is  found  on  the  continent  of  Europe,  in  Sicily,  Val  de 
Travers,  Seyssel,  and  hi  the  United  States  but  to  a  limited  extent 
in  Utah. 

Type  2  is  found  in  Oklahoma,  near  Ravia  and  elsewhere. 

Type  3  occurs  near  Dougherty  in  Oklahoma,  the  rock  being 
a  member  of  the  lower  coal  measures,  according  to  Eldridge,  and 
in  the  neighboring  Buckhorn  District. 

Type  4  is  found  in  Ventura  County,  California. 

Type  5  is  found  in  the  same  locality. 

Type  6  is  unique,  Trinidad  Lake  Asphalt. 

Type  7  includes  large  deposits  of  sand  in  Kentucky  and  Cali- 
fornia, which  are  saturated,  in  situ,  with  a  rather  soft  asphalt. 

Type  8  is  found  wherever  exudations  of  bitumen  have  spread 
over  the  soil  and  become  hardened  by  exposure.  They  are  com- 
mon in  Kern  County,  California. 

It  appears,  therefore,  that  the  character  of  the  mineral  matter, 
with  which  an  asphalt  is  mixed  naturally,  must  be  considered 
as  well  as  the  nature  of  the  bitumen  itself,  in  forming  an  opinion 
of  its  availability  for  paving  purposes. 

With  the  information  which  has  been  presented  in  the  preced- 
ing pages  it  is  now  possible  to  consider  individually  each  of  the 
native  bitumens,  known  generically  or  specifically  as  asphalts, 
and  afterwards  to  make  a  comparative  study  of  their  availability 
in  the  paving  industry. 


THE    SOLID    BITUMENS.  155 

SUMMARY. 

Asphalt  is  a  term  which  may  be  used  either  industrially  01 
specifically;  industrially  to  cover  all  the  solid  native  bitumens 
used  in  the  paving  industry  and  specifically  to  include  only  such 
as  melt  on  the  application  of  heat,  at  about  the  temperature  of 
boiling  water,  are  equally  soluble  in  carbon  disulphide  and  car- 
bon tetrachloride  and  to  a  large  extent  in  88°  naphtha,  those 
hydrocarbons  soluble  in  naphtha  consisting  to  a  very  consider- 
able degree  of  saturated  hydrocarbons,  yielding  about  15  per  cent 
of  fixed  carbon  and  containing  a  high  percentage  of  sulphur. 
Under  this  definition  it  can  be  seen  that  grahamite  is  not  an  asphalt, 
since  it  is  not  largely  soluble  in  naphtha  and  yields  a  very  high 
percentage  of  fixed  carbon  on  ignition.  It  is  also  less  soluble  in 
carbon  tetrachloride  than  in  carbon  disulphide.  Gilsonite  is  not 
an  asphalt,  since  the  saturated  hydrocarbons  contained  in  the 
naphtha  solution  are  very  small  in  amount  and  quite  different 
in  character  from  those  found  in  asphalt. 


CHAPTER  X. 
INDIVIDUAL  ASPHALTS. 

Trinidad  Lake  Asphalt. — In  considering  the  asphalts  indi- 
vidually, it  will  be  best  to  examine  in  detail  the  characteristics 
of  the  one  in  regard  to  which  the  most  is  known  and  with  which 
the  most  successful  pavements  have  been  laid  and  then,  to  com- 
pare others  with  it.  Trinidad  lake  asphalt  is,  of  course,  the 
one  referred  to.  The  location  of  the  deposit  and  the  manner  of 
its  occurrence  may  be  summarized  as  follows:1 

"  The  island  of  Trinidad  lies  off  the  north  coast  of  South 
America,  between  10°  and  11°  of  latitude  and  61°  and  62°  of  longi- 
tude (Fig.  4).  It  is  bounded  on  the  north  by  the  Caribbean  Sea, 
on  the  east  by  the  Atlantic,  on  the  south  by  a  narrow  channel, 
into  which  flow  the  waters  of  the  northern  and  most  westerly 
mouths  of  the  Orinoco,  and  on  the  west  by  the  Gulf  of  Paria, 
the  two  latter  bodies  of  water  separating  it  from  the  mainland 
of  Venezuela.  .  .  . 

"  While  there  are  deposits  of  pitch  scattered  all  over  the  island, 
the  only  ones  of  commercial  importance  are  those  situated  on 
La  Brea  Point,  in  the  wards  of  La  Brea  and  Guapo,  in  the  county 
of  St.  Patrick,  on  the  western  shore  of  the  island.  They  are 
about  28  miles  in  an  air  line  from  Port  of  Spain,  the  seat  of  govern- 
ment, the  chief  harbor  and  only  port  of  entrance,  and  lie  on  the 
north  shore  of  the  southwestern  peninsula,  the  point  upon  which 
they  are  situated  being  apparently  preserved  from  destruction 
by  the  sea,  which  is  elsewhere  rapidly  wearing  away  the  coast 
by  the  bituminous  deposits  which  exist  along  the  shore  and  even 

1  Report  of  the  Inspector  of  Asphalt  and  Cements,  Eng.  Dept.,  District 
of  Columbia,  1892.  On  the  Nature  and  Origin  of  Asphalt,  Long  Island  City, 
N.  Y.,  1898. 

156 


INDIVIDUAL  ASPHALTS. 


157 


some  distance  from  it,  and  which  from  their  toughness  resist  the 
action  of  the  waves  better  than  the  soft  rocks  of  this  region.  The 
pitch  deposits  are  found  scattered  over  the  point,  but  can  be  divided 
conveniently  into  two  classes,  according  to  their  source. 

"  The  main  deposit  is  a  body  of  pitch  known  as  the  Pitch 
Lake,  situated  at  the  highest  part  of  the  point. 

"  Between  this  and  the  sea,  and  more  especially  toward  La 
Brea,  are  other  deposits,  covered  more  or  less  and  mixed  with  soil. 


FIG.  4. 

"  The  pitch  from  these  sources  is  classed  as  '  lake  pitch  '  and 
'  land  pitch/ 

"  By  far  the  largest  amount  of  pitch  is  found  hi  the  pitch  lake, 
originally  nearly  a  circular  area  of  127  acres,  the  surface  of  which, 
in  1894,  was  138.5  feet  above  sea  level.  From  the  lake  the  ground 
falls  away  on  all  sides,  except,  perhaps,  a  slight  ridge  to  the  east 
and  southeast.  In  fact  it  seems  plain  that  this  deposit  lies  in 
the  crater  of  a  large  mud  volcano  which  has  filled  up  with  pitch." 

It  appeared,  when  first  examined  by  the  author  in  1891,  "as 
a  flat,  gently  sloping  mound,  wooded  over  a  large  portion,  open 
savanna  elsewhere,  and  toward  the  northeast  merely  grassed  over. 


158  THE  MODERN  ASPHALT  PAVEMENT. 

"  On  the  west  its  slopes  toward  the  sea  are  gentle  for  some 
distance,,  but  then  more  abrupt.  On  the  north,  toward  La  Brea 
Point,  the  reverse  is  the  case,  and  a  ravine  runs,  with  a  small 
stream,  quite  to  the  village,  this  slope  being  very  scantily  covered 
by  a  growth  of  coarse  grass  near  the  lake,  becoming  more  bushy 
farther  on,  while  the  other  slopes  are  well  wooded,  with  magni- 
ficient  palms  near  the  lake,  forming  a  beautiful  band  or  border 
around  it,  within  which  is  a  grassy  zone  of  about  100  to  200  feet 
or  more  in  width." 

Since  then  the  removal  of  large  quantities  of  pitch  has  quite 
changed  the  surroundings,  owing  to  the  cutting  off  of  the  wood 
and  other  alterations  resulting  from  the  operations  incident  to 
the  exportation  of  asphalt. 

In  1893  a  series  of  borings  were  made  upon  the  lake  by  the 
New  Trinidad  Lake  Asphalt  Company. 

"  A  boring  at  the  center  of  the  lake  was  carried  to  a  depth 
of  135  feet,  the  entire  distance  being  through  pitch,  which,  as 
far  as  ocular  evidence  goes,  has  the  same  character  as  that  at 
the  surface.  It  was  impossible  to  carry  the  boring  deeper,  as 
the  movement  of  the  pitch  had  so  inclined  the  tube — one  foot 
in  six — which  formed  the  lining,  that  it  had  to  be  abandoned. 
It  then  gradually  toppled  over  and  was  engulfed.  Nothing  has 
been  seen  of  it  since.  The  result  was  sufficient,  however,  to  show 
the  great  depth  of  the  crater  and  the  uniformity  of  the  pitch. 
The  depth  attained  was  within  a  few  feet — not  more  than  three 
and  a  half — of  sea  level,  and  yet  we  do  not  know  how  much  deeper 
the  pitch  may  extend.  The  borings  on  the  north  side  of  the  lake 
about  1000  feet  from  the  centre,  and  100  feet  from  the  edge,  was 
in  pitch  of  the  usual  character  for  75  feet,  showing  a  very  steep 
slope  to  the  sides  of  the  crater.  At  80  feet  a  layer  of  fine  white 
sand  was  met  for  a  few  feet,  and  then  asphalt  was  again  encount- 
ered. At  90  feet  sand  mixed  with  asphalt  was  struck,  and  this 
continued  to  a  depth  of  150  feet. 

"  Further  borings,  made  at  some  distance  from  the  lake,  gave 
results  near  the  surface  which  were  similar  to  those  found  at  the 
deeper  levels  at  the  edge  of  the  lake.  Sand,  mixed  with  asphalt 
here  and  there,  was  the  common  material,  while  at  a  depth  of 


INDIVIDUAL  ASPHALTS.  159 

80  feet  on  the  southern  side  of  the  lake,  and  about  80  feet  south 
of  the  road,  and  between  1200  and  1300  fee,t  from  the  centre  of 
the  lake,  a  very  hard  asphaltic  sandstone  was  found. 

"  All  the  evidence  thus  goes  to  show  that  the  sides  of  the  crater 
are  of  sand  or  sandstone,  more  or  less  impregnated  with  bitumen, 
the  sandstone  being  no  doubt  the  rock  of  the  hillside  toward  the 
south,  against  which  the  crater  has  been  built  up. 

"  From  the  borings  it  was  thus  learned  for  the  first  time  how 
enormous  the  deposit  was,  and  the  idea  that  the  mound  was  really 
a  crater  seemed  to  be  confirmed.  It  is,  nevertheless,  hard  to 
realize  that  there  is  at  this  point,  138  feet  above  the  sea,  a  bowl- 
like  depression  over  2300  feet  across,  and  over  135  feet  deep, 
reaching  below  the  sea  level,  and  filled  with  a  uniform  mass  of 
pitch,  which  must  amount  to  over  9,000,000  tons." 

Crude  Trinidad  asphalt  is  an  extremely  uniform  mixture 
or  emulsion  of  gas,  water,  fine  sand,  clay  and  bitumen  which  are 
found  in  the  following  proportions: 

Bitumen 39 .3% 

Mineral  matter 27 .2 

Water  of  hydration  of  clay 3.3 

Water  and  gas,  loss  at  325°  F 29 .0 

98.8% 

The  material  is  of  the  greatest  uniformity  in  composition,  as 
it  has  been  found  that  specimens  collected  at  intervals  of  100  feet 
and  at  a  depth  of  1  foot  over  the  surface  of  the  deposit  and  to  a 
depth  of  135  feet  at  the  centre  all  have  the  same  composition  as 
appears  from  the  following  table. 

The  amount  of  uncombined  water  does  not  appear  among  the 
constituents  in 'these  determinations  as,  in  order  to  avoid  any 
possibility  of  change,  it  was  removed  by  air-drying  at  the  lake 
in  the  course  of  the 'preparation  of  the  samples  for  transportation 
to  the  United  States.  Frequent  examinations  of  the  crude  asphalt 
in  a  fresh  condition  have  shown,  however,  the  water  to  be  as  con- 
stant in  amount  as  the  other  constituents. 

In  this  deposit  there  are,  therefore,  many  millions  of  tons  of 
asphalt  of  a  highly  uniform  composition,  not  only  as  far  as  the 


160 


THE  MODERN  ASPHALT  PAVEMENT. 


AVERAGE  COMPOSITION  OF  TRINIDAD  LAKE  ASPHALT  IN 

CIRCLES. 


Bitumen 

by  CS2. 

Mineral 
Matter 
on 
Ignition. 

Differ- 
ence 
Undeter- 
mined. * 

Soluble 
in 

Naptha.i 

Total 
Bitumen 
thus 
Soluble. 

Circle    2  :    200  feet  from  centre.  . 
4:    400     '                   '    .  . 
6:    600     '                   '     .  . 
"      .8:    800     '                   '     .  . 
"      10:  1000     '                   '     .  . 
"      12:  1100     '                   '     .  . 
General  Average  

55.02% 
54.99 
54.84 
54.66 
54.78 
54.62 
54.92 

35.41% 
35.40 
35.49 
35.56 
35.44 
35.45 
35.46 

9.57% 
9.61 
9.67 
9.78 
9.78 
9.93 
9.72 

31.83% 
31.63 
31.85 
31.67 
31.58 
31.77 
31.72 

57.85% 
57.55 
58.26 
57.97 
57.64 
57.51 
57  79 

Circle  14  :  1400  feet  from  centre.  . 

53.86 

36.38 

9.76 

30.52 

56.66 

AVERAGE  COMPOSITION  OF  TRINIDAD  LAKE  PITCH  FROM 
THE  BORING. 


From  surface  to  135  feet  in  depth. 

54.66% 

35.90% 

9.44% 

31.53% 

57.67% 

>  This  naphtha  possessed  less  solvent  power  than  usual. 

*  Water  of  clay,  not  lost  on  refining,  bitumen  held  by  clay  and  inorganic  salts,  volatil- 
ized on  ignition. 

proportions  of  bitumen  and  mineral  matter  are  concerned,  but 
also  in  the  relation  of  the  malthenes  to  the  asphaltenes. 

Constitution  of  Crude  Trinidad  Asphalt. — The  constitution  of 
the  material  forming  the  great  deposit  found  in  the  Pitch  Lake 
in  the  Island  of  Trinidad  has  only  been  explained  very  recently. 
In  the  course  of  the  ordinary  routine  analysis  of  the  substance 
from  which  the  water  has  been  removed,  it  is  found  that  the 
summation  of  the  percentages  of  bitumen  soluble  in  cold  carbon 
disulphide  and  of  the  mineral  matter  obtained  by  ignition  does 
not  amount  to  100,  as  is  seen  in  the  above  table.  It  has  been  the 
custom  for  many  years  to  call  the  difference  between  this  sum 
and  100  "organic  matter  not  bitumen."  Recent  investigations 
of  the  author  l  have  shown  that  this  is  an  entirely  incorrect  state- 
ment, as  the  asphalt  contains  practically  no  organic  matter  not 


J  The  Proximate  Composition  and  Physical  Structure  of  Trinidad  Asphalt, 
Proc.  Am.  Soc.  Test.  Materials,  1906,  6,  509. 


INDIVIDUAL    ASPHALT.  161 

bitumen,  and  that  the  undetermined  matter  or.  difference  can 
be  readily  explained  as  follows:  » 

Water  and  Gas. — If  a  weighed  amount  of  crude  Trinidad 
asphalt,  immediately  after  being  taken  from  the  deposit,  is  ground 
to  a  fine  powder  and  exposed  to  the  air  for  twenty-four  hours,  it 
will  lose  about  29  per  cent  of  water  and  a  small  additional  amount 
on  further  exposure  in  vacuo  over  sulphuric  acid,  this  latter 
small  amount  being  very  probably  water  of  crystallization  of  the 
salts  which  are  present.  The  total  loss  averages  29  per  cent, 
with  but  very  small  variation,  in  the  fresh  pitch  taken  several 
inches  below  the  surface,  although  on  exposure  to  the  air  for 
some  time  a  very  considerable  proportion  of  this  amount  may  be 
lost,  as  in  the  case  of  storage  of  the  crude  material. 

At  the  same  time  with  the  water  the  gas  which  it  contains 
in  solution,  consisting  of  a  mixture  of  carbon  dioxide  and  hydrogen 
sulphide,  is  lost.  Its  percentage  must  be  extremely  small  by  weight. 

Having  determined  the  average  amount  of  water  in  the  fresh 
pitch  with  some  degree  of  accuracy  it  will  be  convenient  to  con- 
duct the  further  investigation  of  the  pitch  on  the  dried  or  refined 
material. 

Mineral  Matter. — The  residue  of  mineral  matter  obtained 
on  the  ignition  of  refined  Trinidad  asphalt  in  a  muffle  averages, 
as  the  result  of  fifteen  determinations  of  representative  samples, 
36.5  per  cent  corresponding  to  25.9  per  cent  in  the  original  crude 
material,  with  extremes  of  36  and  36.8  per  cent.  As  this  igni- 
tion has  taken  place  at  a  temperature  approaching  800  degrees 
Centigrade,  there  is  every  reason  to  believe  that  considerable 
inorganic  matter  has  been  volatilized,  as  is  often  found  to  be  the 
case  in  the  preparation  of  the  ash  of  vegetable  material.  In  the 
latter  case  the  addition  of  tricalcium  phosphate  prevents  such  loss 
and  it  seemed  that  this  mode  of  procedure  might  be  applicable 
to  the  asphalt.  When  the  latter  was  ignited  in  the  presence  of 
the  phosphate  a  residue  greater  by  2  per  cent  was  obtained,  38.5 
per  cent,  and  one  which  more  correctly  represents  the  percent- 
age of  anhydrous  inorganic  matter  present  in  the  asphalt,  showing 
that  2  per  cent  is  volatilized  in  the  ordinary  course  of  ignition, 
thus  accounting  for  that  amount  of  the  '  'undetermined  matter." 


162 


THE  MODERN  ASPHALT  PAVEMENT. 


The  mineral  matter  on  examination  is  found  by  elutriation  to 
consist  to  a  large  extent,  30  to  40  per  cent,  of  clay  and,  of  course, 
its  water  of  hydration,  which  may  be  properly  regarded  as  a  part 
of  the  mineral  matter  originally  present,  is  lost  on  ignition.  If 
the  residue  after  the  extraction  of  the  asphalt  with  solvents  is 
heated  to  a  temperature  of  340  degrees  Centigrade,  it  loses  from 

4  to   6    per    cent,   the    determination    at  such   a   temperature 
of  course  not  being  one  capable  of  being  made  with  great  accuracy. 
A  certain  amount  of  this  loss  is  plainly  due  to  the  volatilization 
or  destruction  of  bitumen  held  by  the  clay  present,  as  shown  by 
its  condensation  on  the  side  of  a  glass  tube  in  which  the  heating 
is  conducted,  but  as  this  amount,  as  will  appear  later,  cannot 
exceed  1  per  cent,  the  loss  due  to  the  presence  of  water  in  the  clay 
must  reach  at  least  4.5  per  cent.     The  total  loss  on  ignition  of 
bitumen  and  water  in  the  clay  must,  however,  amount  to  about 

5  per  cent  and  be  included  in  the  "undetermined  matter."     When 
this  per  cent  is  added  to  the  2  per  cent  of  inorganic  matter  vol- 
atilized   at    800  degrees    Centigrade,  the   entire    percentage   of 
undetermined  matter  obtained  by  the  usual  method  of  analysis 
is  accounted  for,  so  that  it  appears  that  Trinidad  asphalt  really 
contains  practically  no  organic  matter  not  bitumen. 

In  order  *to  determine  whether  this  assumption  is  correct, 
analyses  have  been  made  of  mixtures  of  an  extremely  pure  bitumen, 
gilsonite,  with  clay  and  other  fine  inorganic  materials,  the  mixture 
being  prepared  by  melting  the  *bitumen,  stirring  being  kept 
up  during  cooling,  and  the  cold  brittle  mixture  being  then  ground 
to  a  fine  powder  in  order  to  obtain  a  uniform  mixture  for 
analysis.  The  results  of  an  examination  of  such  mixtures  by 
the  routine  methods  are  as  follows: 


Bitumen  sol- 
uble in  Car- 
bon Disul- 
phide. 

Mineral 
Residue  on 
Ignition. 

Undeter- 
mined. 

62  3% 

28  8% 

8  9% 

'  '          "      ignited  

59.7 

34.1 

6  2 

72.3 

22.9 

4  8 

'  '        '  '     ignited  

77.9 

17.9 

4  2 

Portland  cement  ignited 

82  6 

15  8 

1  6 

Trinidad  mineral  residue,  ignited  

64.4 

34.3 

1.3 

INDIVIDUAL  ASPHALTS. 


163 


It  appears  from  the  preceding  results  that  all  the  artifical 
mixtures  of  bitumen  and  fine  mineral  matter  apparently  contain, 
as  the  result  of  the  analyses,  a  certain  amount  of  undetermined 
matter  or  organic  matter  not  bitumen,  although  from  the  nature 
of  these  mixtures  nothing  of  this  kind  can  be  present.  The  amount 
varies  from  8.9  per  cent  in  the  case  of  the  unignited  Fullers  earth, 
to  1.3  per  cent  for  the  ignited  mineral  residue  of  Trinidad  asphalt. 
The  larger  percentage  is  due  to  the  presence  of  water  of  hydration 
in  the  Fullers  earth,  while  the  smaller  percentage  shows  that  the 
mineral  matter  in  Trinidad  refined  asphalt  is  capable  of  retaining 
1.3  per  cent  of  bitumen,  either  by  absorption,  adsorption,  or  both. 
Our  assumptions  in  regard  to  the  true  composition  of  Trinidad 
asphalt  are,  therefore,  correct  and  its  actual  composition  should 
be  stated  as  follows: 


Crude  Trinidad 
Asphalt. 

Refined 
Trinidad 
Asphalt. 

Water  and  gas  ...    . 

29  0% 

Bitumen  soluble  in  cold  carbon  disulphide  . 

39  0 

56  5% 

Bitumen  retained  by  mineral  matter  
Mineral    matter,    on    ignition   with   tricalcium 
phosphate  .  .    . 

.3 
27  2 

.3 

38  5 

Water  of  hydration,  clay,  and  silicates  

3  3 

4  2 

* 

98.8% 

99.5% 

Refined  Trinidad  Lake  Asphalt.— Refined  Trinidad  lake  asphalt, 
which  is  dried  with  steam  and  agitated  with  steam,  has  the  charac- 
teristics given  in  the  table  on  pages  164  and  165. 

Refined  Trinidad  Lake  asphalt  is  of  a  homogeneous  structure 
and  uniform  composition  except  in  so  far  as  the  percentage  of 
mineral  matter  and  consequently  of  bitumen  may  vary,  being 
greater  in  one  sample  than  another,  through  sedimentation  caused 
by  the  lack  of  agitation  during  cooling.  It  possesses  none  of  the 
emulsion  structure  seen  in  the  crude  material.  It  has  a  dull 
conchoidal  fracture,  no  lustre,  a  blue-black  color  in  powder  and 


164 


THE    MODERN    AFPHALT   PAVEMENT. 


REFINED    TRINIDAD    LAKE    ASPHALT.     (AVERAGE    COMPO- 
SITION.) 

Test  number 63260 

PHYSICAL    PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original  substance,  dry.  ...  1 .40 

Color  of  powder Blue-black 

Lustre Dull 

Structure Homogeneous 

Fracture. Semi-conchoidal 

Hardness,  original  substance 2 

Odor Asphaltic 

Softens 180°  F. 

Flows 190°  F. 

Penetration  at  78°  F 7° 

CHEMICAL   CHARACTERISTICS. 

Dry  substance : 

Loss,  325°  F.,  7  hours 1.1% 

Character  of  residue, Smooth 

Loss,  400°  F.,  7  hours  (fresh  sample) 4.0% 

Character  of  residue Blistered 

Bitumen  soluble  in  CS2,  air  temperature '. 56 . 53% 

Difference  undetermined 6 . 97 

Inorganic  or  mineral  matter 36 . 50 

>  100.00 
Malthenes : 

Bitumen  soluble  in  88°  naphtha,  air  temperature 35, 6% 

This  is  per  cent  of  total  bitumen 63 . 1 

Per  cent  of  soluble  bitumen  removed  by  H2SO4 61. 3 

Per  cent  of  total  bitumen  as  saturated  hydrocarbons. ...  24 . 4 

Bitumen  soluble  in  62°  naphtha 41 . 7% 

This  is  per  cent  of  total  bitumen 73 . 9 

Carbenes: 

Bitumen  more  soluble  in  carbon  tetrachloride,  air  tem- 
perature, than  in  bisulphide  of  carbon 1.3% 

Bitumen  yields  on  ignition: 

Fixed  carbon. 10.8 

Sulphur 6.2 


INDIVIDUAL     ASPHALTS. 


165 


REFINED   TRINIDAD   LAKE  ASPHALT. 
COMPOSITION.) 


(EXTREMES   IN 


PHYSICAL   PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original  substance,  dry 
Softens                 

1.370 
170°  F. 

1.405 
180°  F. 

Flows      

180°  F. 

190°  F. 

122% 

90% 

CHEMICAL   CHARACTERISTICS. 

Dry  substance  :                                          * 
Loss  325°  F    7  hours                    

1.0% 

1.5% 

Loss  400°  F    7  hours  (fresh  sample) 

4  8% 

3  5% 

Bitumen  soluble  in  CS                         

54.0% 

57.0% 

Malthenes  : 
Per  cent  of  total  bitumen  soluble  in  88°  naphtha, 
air  temperature                   

63.0 

68.  01 

Per  cent  of  total  bitumen  soluble  in  62°  naphtha  .  . 
Bitumen  yields  on  ignition: 

73.0 
11.0 

77.0 
10.0 

1  Percentage  depends  upon  the  character  of  solvent  naptha  and  method  of  treatment. 

an  asphaltic  odor.  It  softens  and  flows  below  the  temperature  of 
boiling  water,  but  becomes  liquid  only  at  much  higher  tempera- 
tures, about  300°  F.  Its  density  is  high  as  compared  with  most 
other  bitumens,  1.40,  owing  to  the  mineral  matter  which  it  contains. 

Refined  Trinidad  asphalt  differs  slightly  in  composition  from 
the  crude  material,  or  rather  from  this  material  after  the  removal, 
without  the  aid  of  heat,  of  the  water  which  it  contains,  owing  to 
the  volatilization,  at  the  higher  temperature  used  in  refining,  of 
certain  constituents  not  driven  off  at  the  temperature  of  boiling 
water. 

The  Mineral  Matter  in  Trinidad  Asphalt. — The  mineral  matter 
in  Trinidad  lake  asphalt  is  as  much  a  fixed  constituent  of  the 
material  as  the  bitumen.  It  is  not  accidental  or  adventitious  as 
it  would  then  vary  in  amount.  It  has  evidently  become  mixed 
with  the  bitumen  under  fixed  and  invariable  conditions  at  some 
subterraneous  point  where  the  bitumen  originates  and  meets  an 
environment  that  results  hi  the  production  of  the  asphalt  itself. 

It  is  in  an  extremely  fine  state  of  subdivision.  On  sifting 
the  particles  are  found  to  be  of  the  size  given  below: 


166  THE    MODERN    ASPHALT   PAVEMENT. 

Passing  200-mesh  sieve 08  mm.         89.8% 

"       100-    "       " 17     "  8.0 

"         80-    "        " 20     "  2.2 

100.0 

And  on  elutriation  of  the  200-mesh  material: 

Subsiding  in  15  seconds,  smaller  than  .08      mm.  24.3% 

"          "    1  minute,        "          "      .05         "  13.1 

"         "30  minutes,      "         "     .025      "  46.7 

After  "       "  "         "     .0075    "  15.9 

100.0 

Under  the  microscope  it  is  found  to  be  composed  principally 
of  quartz  with  clay  and  the  residue  of  the  salts  from  the  mineral 
water  originally  emulsified  with  the  crude  bitumen.  The  quartz  con- 
sists of  very  sharp  flakes,  Fig.  2,  No.  8,  and  their  appearance  leads 
one  to  believe  that  it  has  originally  been  in  solution  under  enormous 
pressure  in  the  thermal  water,  from  which  it  has  separated  on 
the  release  of  the  pressure  or  on  cooling,  and  has  finally  flown 
into  fragments  on  further  reduction  of  the  pressure  to  that  of 
the  atmosphere.  The  presence  of  the  clay  is  more  difficult  to 
explain.  It  is  sufficient  to  know  from  the  point  of  view  of  the 
engineer  that  the  mineral  matter  is  extremely  fine,  is  most  inti- 
mately mixed  with  the  bitumen  by  nature  and  is  consequently 
the  most  perfect  form  of  filler,  far  exceeding  anything  which  can 
be  artificially  mixed  with  a  purer  asphalt,  and  as  such  a  most 
desirable  constituent. 

The  clay,  when  it  has  been  freed  by  treatment  with  acid  from 
the  oxide  of  iron  which  colors  it  the  characteristic  flesh-pink  color 
of  the  ash  of  Trinidad  asphalt  and  which  is  derived  from  the  iron 
salts  in  solution  in  the  thermal  water,  is  a  pure  white,  impalpable 
powder  which  amounts  to  not  more  than  one-third  of  the  entire 
mineral  matter. 

The  mineral  matter  also  contains  constituents,  other  than  the 
iron,  derived  from  the  thermal  water,  principally  sulphates  and 
chlorides  of  soda,  but  as  the  entire  amount  of  salts  in  the  thermal 
water  is  less  than  2  per  cent,  these  so-called  soluble  salts  can  amount 
to  no  more  than  1  per  cent  of  the  refined  asphalt  and  probably 


INDIVIDUAL    ASPHALTS. 


167 


much  less,  as  a  part  is  volatilized  in  refining  and  a  part  rendered 
insoluble.     Actual  extraction  of  the  refined  asphalt  when  most 
thoroughly  carried  out  yields  only  two-tenths  of  1  per  cent  of 
soluble  salts. 
>  The  composition  of  the  mineral  matter  is  as  follows: 


Soluble  in  Acid. 

Insoluble. 

Total. 

Silica,  SiO2  

70.64 

70.64 

Alumina  A12O-                

7.38 

9.66 

17.04 

Ferric  oxide  Fe2O3  *  

6.30 

1.32 

7.62 

Lime  CaO             

0.46 

0.24 

0.70 

0.11 

0.79 

0.90 

Soda,  Na-jO  

1.56 

1.56 

Potassium  K                      .    ... 

0  35 

0  35 

Sulphuric  oxide,  SO3  

0  97 

0  97 

0.22 

0.22 

17.35 

82.65 

100.00 

1  FeO  not  determined. 

Some  of  the  mineral  matter  is  so  impalpably  fine  that  it  will 
not  separate  from  a  solution  of  melted  or  dried  Trinidad  pitch 
in  any  of  the  usual  solvents  even  after  months  of  standing  and 
many  hours'  treatment  in  a  centrifugal.  It  will  pass  also  through 
the  finest  filters.  It  has  been  thought  by  Peckham  and  others,  on 
this  account,  to  be  chemically  combined  with  the  organic  com- 
pounds of  the  asphalt,  but  the  author  has  found  that  by  con- 
tinued swinging  of  a  solution  of  the  asphalt  hi  carbon  disulphide 
in  a  centrifugal  it  can  be  so  far  reduced  that  it  amounts  to  but 
2  per  cent,  and  when  the  bitumen  thus  purified  is  dissolved  in 
chloroform  or  bisulphide  of  carbon  and  passed  through  a  biscuit 
filter  all  the  mineral  matter  is  removed,  leaving  an  absolutely 
pure  bitumen.  This  is  not  surprising,  since  the  smaller  amount 
of  mineral  matter  finally  removed  is  a  ferruginous  clay  and  could 
not  possibly  be  combined  with  the  organic  matter  in  a  chemical 
way,  although  it  no  doubt  is  in  a  state  of  close  physical  combina- 
tion. In  this  connection  the  conclusions  of  Dr.  Allerton  S.  Cush- 
man  of  the  Office  of  Public  Roads  of  the  U.  S.  Department  oi 
Agriculture  on  the  porosity  of  clay  particles  is  of  interest. 


168 


THE    MODERN    ASPHALT    PAVEMENT. 


The  very  finest  mineral  matter  which  is  separated  from  Trini- 
dad lake  asphalt  has  the  following  composition: 

ANALYSIS  OF  FINEST  MINERAL  MATTER. 


Insoluble 
in  HC1. 

Soluble. 

Total. 

SiO2.  . 

32.36 

32.36 

£&-• 

6.74 
1  40 

33.64 

11  74 

40.38 
13  14 

CaO 

45 

3  20 

3  65 

MgO  . 

34 

1  40 

1  83 

K2O  

1  18 

1  18 

Na2O  

.53 

.53 

SO..  . 

7.16 

7.16 

41.29 

58.85 

100.23 

The  Bitumen  of  Trinidad  Lake  Asphalt.— The  bitumen  of  Trin- 
idad lake  asphalt  amounts  to  about  56  per  cent  of  the  refined 
material.  It  is  a  lustrous  black  pitch  like  all  pure  bitumens.  It 
has  a  specific  gravity  of  1.06  to  1.07  and  retains  in  suspension  very 
persistently  amounts  of  the  finest  mineral  matter  of  the  asphalt,  it 
being  only  possible,  as  has  been  shown,  to  remove  this  by  passing  its 
solution  in  bisulphide  of  carbon  through  a  biscuit-filter  of  the  Pasteur 
type.  In  this  way  it  can  be  obtained  in  an  absolutely  pure  form. 
In  this  condition  it  has  the  composition  given  in  table  on  p.  169. 

This  bitumen  is  characterized  by  the  large  percentage  of  sul- 
phur which  it  contains,  and  the  presence  of  nitrogen.  There  are 
apparently  no  oxygen  derivatives  present  in  the  pure  bitumen, 
or  they  occur  in  very  minute  amounts,  that  is  to  say,  they  are 
insoluble  in  chloroform  or  carbon  disulphide. 

It  is  characterized  also  by  its  great  stability  or  lack  of  liability 
to  change  or  volatilize  at  high  temperatures.  When  20  grams 
of  the  materials  are  heated  in  a  glass  crystallizing  dish  to  325°  F., 
according  to  the  method  described  in  Chapter  XXVIII,  it  loses 
but  1  per  cent,  and  only  4  per  cent  when  exposed  to  a  tempera- 
ture of  400°  F.  for  7  hours. 


INDIVIDUAL  ASPHALTS.  169 

TOTAL   BITUMEN    IN   TRINIDAD    LAKE   ASPHALT. 


Preparation. 

I. 

IV. 

V. 

Average. 

82.59 

81.95 

82.44 

82.33 

10.74 

10.51 

10.81 

10.69 

6.04 

6.54 

5.90 

6.16 

0.51 

0.92 

1.00 

0.81 

99.88 

99.92 

100.15 

99.99 

Of  the  total  bitumen  about  63  per  cent,  when  the  process  of 
extraction  is  carried  out  according  to  the  method  described  in 
the  chapter  referred  to,  is  in  the  form  of  hydrocarbons  of  the 
class  known  as  malthenes,  soluble  in  88°  B.  naphtha,  having  a 
density  of  .994.  The  malthenes  are  soft  and  exceedingly  sticky, 
like  maltha.  When  they  are  treated  with  strong  sulphuric  acid, 
according  to  the  author's  method,  all  but  39  per  cent  prove  to 
be  unsaturated  hydrocarbons  which  readily  enter  into  combina- 
tion with  acid.  This  means  that  but  24  to  25  per  cent  of  the 
total  bitumen  in  the  asphalt  consists  of  saturated  hydrocarbons. 
On  ignition  these  malthenes  yield  6.3  per  cent  of  fixed  carbon. 
This  is  about  the  same  percentage  that  is  found  for  the  denser 
California  fluxes  and  for  the  lighter  natural  malthas. 

The  malthenes  can  be  fractioned  in  vacuo  into  hydrocarbons 
of  different  boiling-points,  and  from  them  can  also  be  obtained 
the  nitrogen  and  sulphur  derivatives  corresponding  to  those  found 
by  Mabery  in  the  sulphur  petroleums,  all  of  which  have  been 
described  bv  the  author  elsewhere.1 

It  is  sufficient  to  state  here  that  the  saturated  hydrocarbon  of 
lowest  boiling-point  and  molecular  weight,  which  has  been  sepa- 
rated from  the  malthenes  of  Trinidad  lake  asphalt,  has  the  follow- 
ing properties: 

Boiling-point  at  30  mm 165°  C. 

Specific  gravity  at  25°  C.  .  . 8576 

Refractive  index 1 .4650 

Carbon 86.85% 

Hydrogen 13 . 34 

1  On  the  Nature  and  Origin  of  Asphalt,  Long  Island  City,  N.  Y.,  1898. 


170 


THE  MODERN  ASPHALT  PAVEMENT. 


Such  a  hydrocarbon  would  correspond  to  one  of  the  CnH2n-2 
series  having  the  formula  CisH24,  which  contains  86.67  per  cent 
of  carbon  and  13.33  per  cent  of  hydrogen.  That  this  is  the  formula 
has  been  confirmed  by  determinations  of  the  molecular,  weight 
of  the  substance,  and  its  molecular  refraction.  Of  the  consti- 
tution of  the  hydrocarbons  of  asphalt  something  has  been  said 
in  a  preceding  chapter. 

The  bitumen  of  Trinidad  asphalt  which  is  insoluble  in  88° 
naphtha  is  of  the  class  known  as  the  asphaltenes,  according  to  our 
purely  arbitrary  classification;  the  relative  proportion  of  the  two 
forms  of  bitumen,  asphaltenes  and  malthenes,  being  dependent  upon 
the  nature  of  the  solvent  used,  so  that  any  information  derived  from 
a  determination  of  the  percentages  of  the  two  classes  of  hydro- 
carbons will  be  purely  relative  as  compared  with  other  bitumens 
which  have  been  examined  by  exactly  the  same  methods  and  with 
the  same  solvents.  Trinidad  asphalt  contains  a  very  small  amount 
of  bitumen  which  is  soluble  in  chloroform,  carbon  tetrachloride, 
and  turpentine,  and  which  is  not  soluble  in  carbon  disulphide,  as 
shown  by  Peckham.1 

The  asphaltenes  are  hard,  brittle  bitumens  which  do  not  melt 
but  only  intumesce  on  heating,  and  in  this  respect,  as  well  as  in 
the  percentage  of  fixed  carbon  which  they  yield,  25.8  per  cent., 
correspond  closely  with  the  softer  grahamites.  The  asphaltenes 
are  soluble  in  the  heavy  asphaltic  oils. 

The  ultimate  composition  of  the  malthenes  and  asphaltenes 
in  Trinidad  lake  asphalt  is  as  follows,  as  compared  with  that  of 
the  total  bitumen  previously  given: 


Malthenes. 

Asphaltenes. 

Pure  Bitumen. 

Carbon 

84   6 

82  0 

82  33 

Hydrogen 

11  3 

7  8 

10  69 

Sulphur    .        .        

2  9 

10  9 

6  16 

Nitrogen  

6 

0  81 

99.4 

100.7 

99.99 

Am.  J.  Science,  1896,  [4],  151,  193. 


INDIVIDUAL  ASPHALTS.  171 

The  saturated  hydrocarbons  in  the  malthenes  have  the  follow- 
ing composition: 

Specific  gravity 976 

Carbon 86.40 

Hydrogen 12.70 

Sulphur 45 

Nitrogen 07 

99.62 

From  these  figures  it  appears  that  the  sulphur  derivatives 
are  largely  contained  in  the  asphaltenes  and  in  but  relatively 
small  amounts  in  the  malthenes,  while  they  are  almost  completely 
removed  from  the  latter  by  treatment  with  strong  sulphuric  acid. 
From  the  ultimate  composition  of  the  saturated  hydrocarbons 
contained  in  the  malthenes  it  is  evident  that  these  belong  to  a 
series  in  which  the  number  of  hydrogen  atoms  is  considerably 
below  twice  the  carbon  atoms,  that  is  to  say,  they  must  be  di- 
or  polycyclic  polymethylenes,  and  very  similar  to  those  which 
are  found  in  Texas,  California,  and  other  asphaltic  oils. 

With  the  aid  of  the  above  data  some  insight  may  be  gained 
of  the  character  of  the  bitumen  of  Trinidad  lake  asphalt.  In 
other  asphalts  and  solid  bitumens  the  proportion  of  malthenes 
to  asphaltenes  may  be  greater  or  less,  while  the  amount  of  satur- 
ated hydrocarbons  which  they  contain  may  vary.  '  If  we  accept 
the  bitumen  of  Trinidad  lake  asphalt  as  our  standard  and  refer 
others  to  it,  by  making  the  same  determinations  of  their  character- 
istics as  has  been  done  with  the  type  bitumen,  it  is  possible  to 
differentiate  them  more  or  less  satisfactorily. 

Trinidad  Land  Asphalt. — Of  the  Trinidad  land  asphalt  deposits 
the  author  wrote,  in  1892,  as  follows: 

"  La  Brea  Point  consists  of  a  mass  of  hardened  pitch  deposits 
and  reefs  extending  some  distance  into  the  gulf  and  along  the 
shore  in  both  directions.  The  deposits  are  found  in  greater  or 
less  abundance  at  all  points  between  the  shore  and  the  lake,  and 
directly  along  the  line  of  the  road,  over  an  area  estimated  at  a 
thousand  acres  or  more.  Two  feet  or  more  of  soil  cover  the  deposit 
at  some  distance  from  the  lake,  but  near  it  the  thickness  diminishes 
and  at  places  bare  pitch  is  found. 


172  THE  MODERN  ASPHALT  PAVEMENT. 

"  On  the  point  the  pitch  of  the  reefs  is  hard  and  resonant  and 
has  no  cementitious  value.  The  nearer  the  deposits  are  to  the 
lake,  however,  the  softer  they  become. 

"  The  incline  from  the  lake  to  the  gulf,  a  distance  of  three- 
quarters  of  a  mile,  is  at  first  about  one  in  twenty-five,  gradually 
diminishing  to  the  shore.  Near  the  edge  of  the  lake  there  is  now 
a  rank  growth  of  grass,  followed  by  shrubs  and  trees  after  passing 
the  forks  of  the  road.  In  the  village,  cultivated  land  is  found, 
and  large  pits  filled  with  stagnant  water,  from  which  pitch  has 
been  excavated.  Except  very  near  the  lake,  the  pitch  excavated 
from  the  land  deposits  is  of  a  very  different  appearance  from  that 
taken  from  the  lake,  and  it  is  also  of  several  kinds. 

"  The  conchoidal  masses  removed  from  the  lake,  as  I  have 
said,  contain  large  gas  cavities,  and  in  appearance  and  somewhat 
in  consistency  resemble  a  black  Swiss  cheese.  On  this  account 
the  land  pitch  most  nearly  resembling  this  is  known  as  '  cheese 
pitch.'  It  occurs  in  different  degrees  of  porosity  and  life.  In 
addition,  land  pitch  is  found  in  solid  masses  scarcely  to  be  dis- 
tinguished from  refined  asphalt,  and  this  is  known  as  '  iron  pitch/ 
Pitch,  known  as  '  cokey  pitch/  from  having  been  coked  by  the 
burning  of  the  brush  over  its  surface,  and  the  chocolate  and  friable 
alteration  products  which  have  originated  from  atmospheric 
action  and  disintegration,  are  also  recognized." 

Again  in  another  place  in  the  same  report: 

"  In  past  times  the  pitch  very  probably  continued  to  collect 
(in  the  lake)  until  it  overflowed  the  rim  of  the  crater,  in  many 
directions,  and  thus  perhaps  became  the  source  of  many  of  the 
land  pitch  deposits  now  found  from  the  end  of  the  lake  to  the  sea." 

It  has  also  been  claimed  that  the  land  pitch  has  reached  its 
present  position  by  being  forced  up  through  the  soil  from  the 
same  source  from  which  the  lake  derives  its  material. 

For  the  purpose  of  looking  into  the  nature  of  the  material 
from  the  point  of  view  of  its  suitability  for  the  asphalt  paving 
industry  this  is  immaterial.  It  is  the  nature  and  characteristics 
of  the  land  asphalt  deposits  as  they  are  available  commercially 
which  are  of  interest  at  this  point. 

Trinidad  land  asphalt  differs  from  that  found  in  the  lake  deposit 


INDIVIDUAL  ASPHALTS.  173 

as  the  result  of  such  changes  as  have  been  brought  about  by  its 
having  been  buried  under  soil  and  exposed  to  the  action  of  ground- 
water  and  aging  for  many  centuries,  that  is  to  say,  it  is  a  very 
much  weathered  material.  The  two  materials  are  undoubtedly 
derived  from  the  same  original  subterranean  source.  The  land 
asphalt  may,  as  has  been  said,  have  reached  its  present  position 
either  by  overflow  from  the  lake  or  by  intrusion  into  its  present 
position  in  the  soil  directly  from  the  point  of  origin.  In  either 
case  no  land  asphalt  has  been  found  which  has  not  been  altered 
in  its  nature  owing  to  its  present  or  past  environment,  so  that 
it  differs  essentially  from  the  lake  material. 

Land  asphalt  is  very  variable  in  character,  depending  upon  the 
length  of  time  during  which  it  has  been  subjected  to  weathering.  It 
is  much  less  cheesy  than  lake  asphalt,  that  is  to  say,  it  contains 
a  smaller  number  of  gas  cavities,  and  is  harder.  Some  of  it  has 
been  converted  by  brush  fires  into  a  hard  compact  pitch  without 
gas  cavities,  resembling  refined  asphalt  which,  from  its  hardness, 
is  known  as  iron  pitch.  Some  portion  of  the  land  asphalt  has 
been  converted  even  to  coke.  These  two  latter  forms  are  of  no 
interest  to  the  paving  industry  and  are  carefully  removed  from 
the  material  which  is  collected  for  this  purpose.  Further  weather- 
ing of  the  material  from  the  action  of  soil-water  converts  it  into 
a  substance  of  a  chocolate  color,  which  is  very  friable.  Where 
the  weathering  is  carried  to  its  ultimate  conclusion  only  the  fer- 
ruginous mineral  matter  is  left,  of  a  bright-red  color,  as  is  evident 
on  the  beach;  where  the  asphalt  is  subjected  to  the  continuous 
action  of  sea  water  it  becomes  very  hard  but  is  not  weathered 
to  any  further  degree.  That  is  to  say,  water  containing  the  salts 
found  in  sea  water  does  not  act  upon  it.  This  is  important  in 
connection  with  the  claims  that  soluble  salts  cause  disintegration 
of  Trinidad  asphalt. 

Much  of  the  asphalt  found  in  the  land  deposits  plainly  orig- 
inated in  the  so-called  lake  and  is  now  found  mingled  with  the 
soil  after  it  has  run  over  the  rim  of  the  lake.  In  consequence, 
the  land  asphalt  nearest  the  lake  is  much  less  weathered  than 
that  at  a  distance.  The  difference  can  be  seen  from  the  following 
analyses  of  specimens  collected  near  the  lake  and  at  intervals 


174 


THE  MODERN  ASPHALT  PAVEMENT. 


between  it  and  the  shore.     For  comparison  an  analysis  of  lake 
asphalt  is  given: 

AVERAGE   COMPOSITION   OF   LAKE   PITCH,   DRIED   IN   VACUO, 
KEARNEY  COLLECTION. 


Bitumen 
Soluble  CS2. 

Mineral 
Matter. 

Difference 
Undeter- 
mined. 

Bitumen 
Soluble 
Petroleum 
Naphtha. 

Total 
Bitumen 
Soluble  in 
Naphtha. 

Average  

54.25% 

36.51% 

9.24% 

35.41% 

65.27% 

AVERAGE   COMPOSITION    OF   LAND   PITCH,   DRIED   IN   VACUO, 

KEARNEY  COLLECTION. 
Ei^ht  specimens  from  Lot  C. ,  near  the  lake. 


Average 


54.03% 


36.49% 


9.48% 


33.02% 


Four  specimens  from  Crown  Land  Lots  adjoining  C. 


Average. 


53.81% 


36.62% 


9.57% 


32.29% 


Five  specimens  from  east  of  road,  middle  ground. 


Average 


52.31% 


37.80% 


9.89% 


7o 


31.25% 


61.11% 


60.01% 


59.74% 


Seven  specimens  from  Village  Lots,  near  the  Gulf. 


Average  
General  average. 

52.27% 
53.10 

37.73% 
37.16 

10.01% 
9.74 

31-42% 
31.99 

60.12% 
60.14 

It  is  apparent  that  the  effect  of  weathering  has  been  com- 
paratively small  in  the  deposits  closely  adjoining  the  lake,  but 
that,  as  we  proceed  further  on  toward  the  shore,  the  change  is 
more  marked  and  is  particularly  evidenced  by  the  decrease  in 
bitumen  present,  and  decrease  in  the  percentage  of  malthenes. 
The  lake  pitch,  so-called,  has,  with  the  naphtha  used  as  a  solvent, 
65.3  per  cent  of  its  bitumen  soluble  in  naphtha,  while  just  outside 
the  lake  the  land  pitch  has  only  61.1  per  cent,  and  further  on  only 
59.7  per  cent  soluble.  This  may  seem  a  small  difference,  but  it 


INDIVIDUAL  ASPHALTS.  175 

is  evidence  of  a  large  change.  In  glance  pitch,  examined  in  the 
same  way,  24  per  cent  only  of  the  entire  bitumen  was  found  to 
be  soluble  in  naphtha,  in  lake  pitch  65.3  per  cent.  Land  pitch 
may,  therefore,  be  inferred  to  be  partly  converted  from  lake  to 
glance  pitch. 

The  composition  of  an  average  commercial  refined  land 
asphalt  as  compared  with  the  average  lake  material  is  well  shown 
in  the  table  on  page  176. 

Land  asphalt  being  so  dependent  upon  its  environment  for 
its  character,  it  is  hardly  possible  to  determine  its  average  com- 
position. The  extremes  which  are  met  with  in  recent  commer- 
cial supplies  are  of  interest  (see  table,  page  177). 

From  these  figures  it  appears  that  refined  Trinidad  land 
asphalt  of  good  quality  is  differentiated  from  the  lake  supply  by  its 
higher  specific  gravity,  owing  to  the  rather  larger  amount  of  mineral 
matter  which  it  contains,  by  a  higher  softening  or  melting-point, 
and  somewhat  lower  percentage  of  bitumen  and,  in  consequence  of 
these  facts,  a  much  greater  hardness  at  all  temperatures. 

Naturally  the  percentage  of  malthenes  is  smaller  in  the  land 
than  in  the  lake  asphalt  and  that  of  fixed  carbon  slightly  higher. 

The  ultimate  composition  of  the  pure  bitumen  of  land  asphalt  as 
compared  with  that  of  lake  is  given  in  the  second  table  on  page  177. 

The  weathering  of  the  bitumen  has,  therefore,  produced  essen- 
tial changes  in  the  composition  of  the  material,  there  having 
been  a  loss  of  sulphur,  probably  due  to  its  elimination  as  hydro- 
gen sulphide,  and  an  increase  in  carbon,  due  to  the  same  cause 
and  to  the  elimination  of  hydrogen  as  water  during  the  process  of 
condensation. 

These  differences,  though  small  in  themselves,  are  indicative 
of  the  fact  that  the  weathered  land  asphalt  is  not  the  same  in 
its  character  as  the  fresh  lake  material.  In  themselves  they 
would  not  amo'unt  to  a  great  deal  unless  confirmed  by  actual 
results  obtained  in  the  use  of  the  material  industrially.  As  a 
matter  of  fact,  such  confirmation  is  not  lacking  if  land  is  used  in 
the  same  way  as  lake  asphalt,  that  is  to  say,  if  fluxed  to  an  asphalt 
cement  with  ordinary  paraffine  petroleum  residuum.  In  the 
preparation  of  such  an  asphalt  cement  the  striking  differences 


176 


VTHE  MODERN   ASPHALT  PAVEMENT. 
REFINED  TRINIDAD  LAND  ASPHALT. 


63260 

36721 

Lake  R.  A. 

Land  R  A 

PHYSICAL   PROPERTIES. 

Specific  gravity,  78°  F,/78°  F.,  original  sub- 
stance  dry         .          .  «              . 

1  40 

1  .4196 

Color  of  powder  or  streak  

Blue-black 

Brown-black 

Lustre           

Dull 

Dull 

Homogeneous 

Homogeneous 

Semi- 

Semi- 

Odor  

conchoidal 
Asphaltic 

conchoidal 
Asphaltic 

Softens  

180°  F. 

188°  F 

Flows  .                     ....           

190°  F 

198°  F 

Penetration  at  78°  F    

7° 

0° 

CHEMICAL   CHARACTERISTICS. 

Dry  substance: 
Loss,  325°  F  ,  7  hours 

1  1% 

1  0% 

Character  of  residue   

Smooth 

Blistered 

Loss,  400°  F.  ,  7  hours  (fresh  sample)  

4  0% 

3  0% 

Character  of  residue  

Blistered 

Blistered 

Bitumen  soluble  in  CS2,  air  temperature  
Difference 

56.53% 
6  97 

54.1% 
7  9 

Inorganic  or  mineral  matter  

36  50 

38  0 

Malthenes: 
Bitumen  soluble  in  88°  naphtha,  air  tem- 
perature              

100.0 
35  6% 

100.0 
33  5% 

This  is  per  cent  of  total  bitumen  

63.1 

61  9 

Per  cent  of  soluble  bitumen  removed  by 
H2SO4  

61.3 

64.8 

Per  cent  of  total  bitumen  as  saturated  hy- 
drocarbons    

24  4 

21  8 

Bitumen  soluble  in  62°  naphtha  

41  7% 

38  2% 

This  is  per  cent  of  total  bitumen  

73.9 

70.6 

Carbenes: 
Bitumen    more   soluble   in   carbon   tetra- 

1  3% 

0  0% 

Bitumen  yields  on  ignition: 
Fixed  carbon  

108% 

129% 

Sulphur  

6.2% 

5.0% 

INDIVIDUAL  ASPHALTS. 


177 


REFINED   TRINIDAD   LAND   ASPHALT.      (EXTREMES   IN 
COMPOSITION.) 


PHYSICAL   PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original  substance, 
drv 

1.400 

1.450 

Softens  

188°  F. 

220°  F. 

Flows    

198°  F. 

230°  F. 

Flow  in  per  cent  of  Trinidad  lake  =  100%  

CHEMICAL   CHARACTERISTICS. 

Bitumen  soluble  in  CS2  air  temperature 

83% 
55  0% 

15% 
52  0% 

Difference       .             

7.5 

9.5 

Inorganic  or  mineral  matter     

37.5 

38.5 

Per  cent  of  total  bitumen  soluble  in  88°  naphtha, 
air  temperature 

100.0 
63  0 

100.0 
52.0 

Per  cent  of  soluble  bitumen  removed  by  H-jSO.  .  .  . 
Per  cent  of  total  bitumen  soluble  in  62°  naphtha  .  . 

Bitumen  yields  on  ignition: 

62.0 
71.0 

12.9 

64.8 
60.0 

14.0 

COMPARISON  OF  ULTIMATE  COMPOSITION  OF  PURE 
BITUMEN,  TRINIDAD  LAND  AND  LAKE  ASPHALT. 


Land. 

Lake. 

Carbon              

83  7 

82.33 

Hydrogen     

10  8 

10.69 

Sulphur  

5.1 

6.16 

Nitrogen  

0.5 

0.81 

100.1 

99.99 

between  lake  and  land  asphalt  are  brought  out  by  the  fact  that 
where  20  pounds  of  a  good  paraffine  residuum  is  sufficient  to  make 
a  suitable  asphalt  cement  when  added  to  each  100  pounds  of  lake 
asphalt,  as  much  as  30  or  more  pounds  of  the  same  residuum  are 
required  to  make  a  cement  of  the  same  consistency  with  land 
asphalt.  Extended  experience  with  surfaces  laid  with  these  two 
asphalt  cements  has  shown  that  after  3  or  4  years  service  the 
surface  laid  with  the  land  asphalt  begins  to  show  signs  of  deterio- 
ration and  often  at  even  shorter  periods.  Our  practical  results, 
therefore,  confirm  those  obtained  in  the  laboratory  even  more 
strikingly  than  might  be  expected. 


178  THE  MODERN  ASPHALT  PAVEMENT. 

Land  asphalt,  as  has  been  seen,  contains  a  very  much  weathered 
and  hardened  bitumen,  much  more  hardened  than  one  would  be 
led  to  believe  from  mere  analytical  results  and  only  shown  by 
the  necessity  for  the  use  of  half  as  much  again  of  flux  in  making  a 
cement,  and  by  the  fact  that  when  cylinders  of  the  two  asphalts 
of  the  same  size  are  placed  upon  a  corrugated  brass  plate  and 
exposed  to  a  high  temperature,  at  an  angle  of  45°,  the  land  asphalt 
flows  from  but  20  to  50  per  cent  as  far  in  a  given  time  as  is  the 
case  with  the  lake  asphalt.  This  is,  of  course,  due  to  the  absence 
of  the  softer  hydrocarbons  of  the  malthene  series  which,  in  the 
lake  asphalt,  are  very  susceptible  to  increase  of  temperature  and 
consequently  occasion  the  more  rapid  flow  of  the  latter.  The 
absence  of  these  malthenes  in  a  paving  cement  is  a  serious  deficiency. 

The  recent  advent  of  the  heavy  asphaltic  oils  as  fluxes  makes 
it  possible,  however,  to  supply  to  a  certain  extent  the  deficiencies 
in  the  bitumen  of  land  asphalt  by  the  addition  of  a  suitable  amount 
of  such  flux,  instead  of  producing  the  required  softness  with  a 
great  excess  of  paraffine  residuum,  thus  forming  an  unbalanced 
cement.  Pavements  made  with  such  an  asphalt  cement  have 
been  fairly  satisfactory,  but  are,  unfortunately,  uneven  in  char- 
acter owing  to  the  lack  of  uniformity  of  the  original  land  asphalt, 
and  to  the  large  amount  of  skill  which  must  be  used  in  combining 
the  different  ingredients  and  to  the  care  which  the  production  of 
a  uniform  asphalt  cement  from  such  materials  presents. 

Bermudez  Asphalt. — The  occurrence  of  a  deposit  of  asphalt 
in  what  has  been  called  the  Bermudez  "  Pitch  Lake,"  in  the  State 
of  Sucre,  formerly  Bermudez,  in  Venezuela,  Fig.  4,  has  been 
described  by  the  author  in  another  place  as  follows:1 

"  From  the  mouth  of  the  Orinoco,  the  northeastern  coast  of 
Venezuela,  which  faces  Trinidad,  is  low  and  consists  of  vast  man- 
grove swamps,  through  which  run  deep  tidal  estuaries.  That  por- 
tion forming  part  of  the  State  of  Bermudez  extends  inland  for  many 
miles.  It  lies  on  the  opposite  side  of  the  Gulf  of  Paria  from  Trini- 
dad. About  30  miles  in  an  air-line  from  the  coast  the  asphalt 
deposit,  known  as  the  Bermudez  Pitch  Lake,  is  found  at  the  point 
where  a  northern  range  of  foot  hills  comes  down  to  the  swamp. 

1  On  the  Nature  and  Origin  of  Asphalt,  Long  Island  City,  N.  Y.,  1898, 


INDIVIDUAL  ASPHALTS.  179 

The  Guanaco  River,  a  branch  of  the  San  Juan,  one  of  the  large 
canos  or  estuaries  of  this  region,  at  about  65  miles  in  its  winding 
course,  from  its  mouth,  runs  within  3  miles  of  the  deposit,  but 
it  is  5  or  6  miles  to  a  suitable  wharfage  site.  On  the  other  hand, 
towards  the  north  a  road  runs  to  the  hills  and  to  the  village  of 
Guaryquen.  These  are  the  means  of  communication  with  the 
deposit.  The  so-called  lake  is  situated  between  the  edge  of  the 
swamp  and  the  foot  hills  in  what  might  be  termed  a  savanna.  It 
is  an  irregular-shaped  surface  with  a  width  of  about  a  mile  and  a 
half  from  north  to  south  and  about  a  mile  east  and  west.  Its  area 
is  a  little  more  than  900  acres,  and  it  is  covered  with  vegetation, 
high  rank  grass,  and  shrubs,  1  to  8  feet  high,  with  groves  of  large 
moriche  palms,  called  morichales.  One  sees  no  dark  expanse  of 
pitch  on  approaching  it  as  at  the  Trinidad  pitch  lake,  and  except 
at  certain  points  where  soft  pitch  is  welling  up,  nothing  of  the 
kind  can  be  found.  The  level  of  the  surface  of  the  deposit  does 
not  vary  more  than  2  feet  and  is  largely  the  same  as  that  of  the 
surrounding  swamps.  In  the  rainy  season  it  is  mostly  flooded 
and  at  all  times  very  wet,  so  that  any  excavation  will  fill  up  with 
water.  These  conditions  make  it  difficult  to  get  about  upon  it 
or  to  excavate  pitch  easily. 

"  It  is  readily  seen  that  this  deposit  is  a  very  different  one  from 
that  in  the  pitch  lake  of  Trinidad.  It  seems  to  be  in  fact  merely  an 
overflow  of  soft  pitch  from  several  springs  over  this  large  expanse 
of  savanna  and  one  which  has  not  the  depth  or  uniformity  of  that  at 
Trinidad. 

"  Being  on  a  level  with  the  mangrove  swamps  and  with  foot  hills 
on  its  other  side,  any  large  amount  of  asphalt  could  hardly  be  held 
in  position  here,  as  in  the  old  crater  in  Trinidad,  but  would  burst 
out  into  the  swamp  and  be  lost,  and,  as  far  as  borings  have  been 
made,  they  seem  to  indicate  but  a  small  depth  anywhere  as  com- 
pared with  that  of  the  Trinidad  lake. 

"  At  different  points  there  is  at  most  a  depth  of  7  feet  of  mate- 
rial, while  the  deepest  part  of  the  soft  maltha  is  only  9  feet  and 
the  average  of  pitch  below  the  soil  and  coke  only  4  feet.  At  points 
there*  is  not  more  than  2  feet  of  pitch,  and  in  the  morichales  or 
palm  groves  it  is  often  5  feet  below  the  surface.  At  several  points, 


180  THE  MODERN  ASPHALT  PAVEMENT. 

scattered  over  the  surface,  are  areas  of  soft  pitch,  or  pitch  that 
is  just  exuding  from  springs.  The  largest  area  is  about  7  acres 
in  extent  and  of  irregular  shape.  This  has  little  or  no  vegetation 
upon  it,  and  from  the  constant  evolution  of  fresh  pitch  is  raised 
several  feet  above  the  level  of  the  rest  of  the  deposit.  This  soft 
asphalt  has  become  hardened  at  the  edges,  but  when  exposed 
to  the  sun  is  too  soft  to  walk  upon.  The  material  is  of  the  nature 
of  a  maltha  and  it  is  evidently  the  source  of  all  the  asphalt  in  the 
lake,  from  these  exudations  the  pitch  having  spread  in  every 
direction,  so  that  no  great  depth  of  pitch  is  found  even  at  this  point. 

"  A  careful  examination  of  the  surroundings  shows  that  in 
one  respect  there  is  a  resemblance  between  the  point  of  evolution 
of  the  soft  pitch  at  the  Bermudez  and  at  the  Trinidad  lakes.  Gas 
is  given  off  in  considerable  quantities  at  both  places,  and  in  both 
cases  consists  partly,  at  least,  of  hydrogen  sulphide.  At  the 
Bermudez  lake  I  was  unable  to  determine  whether  it  was  accom- 
panied by  carbonic  dioxide,  but  the  odor  of  hydrogen  sulphide 
was  strong. 

"  The  consistency  of  the  soft  pitch  at  the  centre  of  the  Ber- 
mudez lake  is  much  thinner  than  that  of  the  Trinidad  lake.  It 
will  run  like  a  heavy  tar  and  does  not  evolve  gas  in  the  same  rapid 
way  or  harden  as  quickly  after  collection.  It  therefore  does  not 
retain  the  gas  which  is  generated  in  it,  nor  does  the  deposit  as  a 
whole  do  so  to  the  same  extent  as  the  Trinidad  pitch.  Where, 
however,  the  surface  of  the  soft  pitch  has  toughened  by  exposure 
to  the  sun  and  air  and  where  gas  is  given  off  beneath  it,  it  is  often 
raised  in  dome-like  protuberances,  the  beehives  which  were  spoken 
of  by  early  visitors  to  the  Trinidad  lake.  These  have  a  thin  wall  of 
pitch  and  are  filled  with  gas  which  readily  burns,  and  have  been 
seen  two  feet  or  more  in  height  and  18  inches  in  diameter.  They 
are,  of  course,  found  only  near  the  soft  spots. 

"  Although  the  pitch  at  the  Bermudez  lake  is  too  soft  to  entangle 
and  hold  permanently  the  gas  which  is  given  off,  where  the  pitch 
of  medium  consistency  is  covered  with  water  it  does  not  escape 
so  readily,  and  thus  often  raises  in  the  pools  of  water  a  mushroom- 
like  growth  of  pitch  by  the  reduction  of  the  gravity  of  the  friass 
from  the  included  gases.  These  mushrooms  correspond  completely, 


INDIVIDUAL  ASPHALTS.  181 

except  in  size,  with  those  described  by  Manross  as  existing  at  the 
Trinidad  lake  when  he  visited  it.  It  seems,  therefore,  that  we 
have  to-day  several  of  the  phenomena  represented  at  the  Venezue- 
lan lake  which  the  hand  of  man  has  destroyed  at  Trinidad. 

"  There  is,  however,  no  evidence  of  the  same  simultaneous 
boiling  up  of  water  with  the  fresh  soft  pitch  that  has  been  deter- 
mined at  the  Trinidad  lake,  but  that  there  is  none  at  all  is  not 
certain,  as  at  the  tune  I  visited  the  locality  heavy  rains  were  fall- 
ing which  prevented  the  detection  of  a  small  amount.  It  seems, 
however,  improbable,  as  the  soft  pitch  contains  little  or  no  water 
and  the  traces  found  in  the  samples  collected  are  probably  derived 
from  rain. 

"  Hardening  of  the  Main  Mass  of  Pitch. — The  soft  pitch,  after 
it  exudes  at  the  centre  of  the  Bermudez  lake,  undoubtedly  hardens 
slowly  on  exposure,  but  the  condition  of  the  surface  of  the  main 
mass,  which  is  very  hard  and  rough,  and  of  the  harder  borders 
of  the  soft  spots  is  due  to  other  causes  also. 

"  The  edges  of  the  areas  of  soft  asphalt  are  covered  here  and 
there  with  masses  of  glance  pitch  and  with  black  and  brittle  cin- 
ders or  coke,  and  which  seem  to  have  been  produced  from  the 
maltha  by  fire.  This  is  evidently  the  case,  since  the  rank  growth  of 
grass  which  is  very  dry  in  the  dry  season  is  particularly  adapted 
for  a  rapid  and  intense  combustion.  Such  fires  have  been  even 
recently  started  intentionally  and  accidentally  and  to  them  are 
due  the  condition  of  the  present  surface  of  the  deposit  and  the 
character  of  much  of  the  pitch. 

"  The  general  surface  of  the  lake  is  very  irregular  and  hard. 
There  are  many  very  narrow :  and  irregular  channels  or  depres- 
sions from  a  few  inches  to  4  feet  deep,  filled  with  water,  and  not 
being  easily  distinguished,  one  often  falls  into  them.  At  the  foot 
of  the  growth  of  grass  and  shrubs  are  ridges  of  pitch  mingled  with 
soil  and  decayed  vegetation,  which  have  been  plainly  coked  and 
hardened  by  fires  of  the  nature  which  have  been  mentioned.  When 
this  hardened  material  which  forms  only  a  crust  is  removed,  asphalt 
of  a  kind  suitable  for  paving  is  found.  The  crust  is  from  1%  to 
2  feet  in  depth  and  very  firm,  while  the  asphalt  underneath  would 
not  begin  to  sustain  the  weight  which  that  of  the  Trinidad  pitch 


182  THE  MODERN  ASPHALT  PAVEMENT. 

lake  does  easily.  There  are  breaks  in  the  crust  here  and  there 
through  which  soft  pitch  exudes  as  has  been  described. 

"  It  appears,  therefore,  that  the  Bermudez  deposit  owes  its 
existence  to  the  exudation  of  a  large  quantity  of  soft  maltha, 
which  is  still  going  on  and  which  has  spread  over  a  great  extent; 
that  this  has  hardened  spontaneously  in  the  sun,  and  has  also, 
by  the  action  of  fire,  been  converted  over  almost  the  entire  sur- 
face into  a  cokey  crust  of  some  depth,  beneath  which  the  best 
material  lies  and  that  here  and  there  are  scattered  masses  of  glance 
pitch  produced  in  a  similar  way  from  less  violent  action  of  heat. 
There  is  no  evidence  of  a  general  movement  and  mingling  of  the 
mass  of  this  deposit  in  any  way  that  would  produce  a  uniformity 
of  composition  as  seen  in  the  Trinidad  pitch  lake,  although  there 
is  a  certain  amount  of  gas  evolved  at  the  soft  spots  where  maltha 
exudes  and  some  gas  cavities  are  found  in  the  general  mass  of 
the  pitch  beneath  the  crust." 

The  original  Bermudez  pitch,  as  it  exudes  at  the  soft  spots, 
contains  no  mineral  matter  or  water  and  is  consequently  an 
extremely  pure  bitumen.  It  has  the  following  ultimate  com- 
position: 

Carbon 82.88% 

Hydrogen 10 .79 

Sulphur 5.87 

Nitrogen . . .          .75 

100.29 

As  in  the  case  of  the  bitumen  of  Trinidad  asphalt,  sulphur  plays 
an  important  role  in  its  composition,  but  in  the  asphalt  as  it  is 
used  commercially  much  of  this  sulphur  has  disappeared,  having 
been  evolved  as  hydrogen  sulphide,  the  industrial  material  con- 
taining less  than  4  per  cent. 

Exposure  of  the  soft  maltha  to  the  sun,  after  its  evolution 
and  chemical  changes,  hardens  the  material  somewhat.  The  com- 
mercial supply  has,  however,  been  largely  altered,  owing  to  the 
fact  that  the  rank  vegetable  growth  which  extends  over  the  900 
or  1000  acres  of  the  deposit  has  frequently  been  set  on  fire,  either 
accidentally  or  intentionally,  with  the  production  of  such  a  degree 
of  heat  as  to  convert  much  of  the  material  on  the  surface  to  coke 


INDIVIDUAL  ASPHALTS. 


183 


and  that  below  to  a  harder  form  of  bitumen  than  that  of  the  orig- 
inal maltha.  It  is,  of  course,  very  evident  that  this  conversion 
has  not  been  uniform  and  that  the  product  taken  from  the  lake 
cannot,  on  this  account,  be  in  itself  uniform.  In  a  collection  of 
some  forty  samples  taken  in  1896,  the  following  extremes  of  com- 
position were  found: 

EXTREMES   IN   THE   COMPOSITION   OF   CRUDE   BERMUDEZ 

ASPHALT. 


Highest. 

Lowest. 

CRUDE    SUBSTANCE. 

Loss  212°  F    4  days 

46  20% 

10  72% 

'  '      400°  F    7  hours                           

13.60 

4  72 

DRIED    SUBSTANCE. 

Specific  gravity  78°  F  /78°  F 

1  075 

1  005 

Loss  400°  F    7  hours        

16  05 

5  81 

Softens                    

170°  F 

140°  F. 

Flows        *  

lg8°F. 

135°  F. 

Bitumen  soluble  in  CS^  air  temperature 

98  52% 

90  65% 

Difference 

6  45 

0  62 

Inorganic  or  mineral  matter 

3  65 

0  50 

Bitumen  soluble,  88°  naphtha,  air  temperature.  .  .  . 
This  is  per  cent  of  total  bitumen  

73.05 
76.55 

63.40 

67.78 

The  asphalt  as  it  occurs  in  the  deposit  holds  from  46  to  10  per 
cent  of  water  and  3.6  to  .5  per  cent  of  mineral  matter.  These 
substances  as  well  as  the  undetermined  material,  amounting 
to  from  6  to  .6  per  cent,  must  be  adventitious,  and  are  in  part,  at 
least,  derived  from  the  vegetation  with  which  it  comes  in  contact 
and,  although  some  of  the  organic  matter  is  due  to  the  conversion 
of  part  of  the  bitumen  to  coke  by  fires,  the  greater  portion  con- 
sists of  roots  of  grasses  and  shrubs  which  penetrate  the  asphalt 
with  ease. 

The  wide  variation  in  the  character  of  the  material  in  differ- 
ent parts  of  the  deposit  is  therefore  made  evident  by  the  above 
figures.  The  high  percentage  of  undetermined  matter  is  not,  as 
in  Trinidad  asphalt,  due  to  the  presence  of  clay  or  volatile  inor- 
ganic salts. 

There  are  other  evidences  of  this  variation  derived  from  the 


184 


THE  MODERN  ASPHALT  PAVEMENT. 


examination  of  various  cargoes  of  Bermudez  asphalt  which  have 
been  brought  to  this  country  for  commercial  use. 


Crude. 

After  Drying. 

Year. 

Water. 

Bitumen 

Soluble 
in  CS2. 

Difference 
Undeter- 
mined. 

Inorganic  or 
Mineral 
Matter. 

1898       

15.8% 

95.7% 

2.3% 

2.0% 

1899  

19.8 

92.5 

4.3 

3.0 

1901  

95.0 

2.5 

2.5 

sample 

23  9 

95  7 

2  8 

1.5 

1902  {  Poor 

<  i 

53  2 

89.2 

9.0 

1.8 

1  QO**  /  G°°d 

1903  \  Poor 

sample  

<  < 

29.9 
33.3 

97.0 
95.5 

1.5 
2.9 

1.5 
1.6 

Refined  Bermudez  Asphalt. — When  the  crude  Bermudez  asphalt, 
as  it  is  taken  from  the  deposit,  is  melted  and  dried  it  becomes  the 
refined  Bermudez  asphalt  of  commerce  and  it  is,  of  course,  vari- 
able in  character  like  the  crude  material  it  is  derived  from.  The 
loss  of  light  oils  in  the  softer  material  has  a  tendency  to  bring  all 
the  refined  asphalt  more  nearly  to  a  uniform  condition  than  would 
be  expected.  There  are,  however,  decided  differences  not  only 
as  regards  its  physical  characteristics  but  also  chemically. 

The  variation  in  the  consistency  is  well  shown  by  the  relative 
length  to  which  various  lots  of  this  asphalt  will  flow  on  an  inclined 
plane  at  temperatures  above  the  softening  point.  For  several 
cargoes  in  this  way  the  following  data  were  obtained: 

PER  CENT  OF  FLOW. 

Original  material  in  use  in  Washington,  D.  C. , 

1893 100.0% 

Importation  of  1895 73 . 5 

"  "  1898 73.0 

"  "  March,  1899 50.0 

"  "  May        "    41.6 

"  "  June       "    73.3 

"  "  1903 125.0 

From  the  preceding  figures  it  appears  that  while  the  first  mate- 
rial brought  to  this  country  was  quite  soft,  the  refined  asphalt 
became  harder  in  subsequent  years  and  recently  is  again  softer, 


INDIVIDUAL  ASPHALTS.  185 

owing  to  the  fact  that  the  crude  asphalt  has  been  collected  of 
late  at  points  nearer  the  maltha  springs. 

In  consequence  of  this  every  lot  of  Bermudez  asphalt  must  be 
handled  in  its  own  peculiar  way,  and  in  this  respect  it  compares 
unfavorably  with  Trinidad  lake  asphalt  which  is,  as  has  been 
seen,  extremely  uniform. 

The  percentage  of  bitumen  in  the  refined  material  varies  as 
well  as  the  consistency,  ranging  from  93  to  97  per  cent,  but  will 
usually  average  95  per  cent. 

The  data  given  in  the  tables  on  pages  186  and  187  show  the 
physical  properties  and  approximate  chemical  composition  of  refined 
Bermudez  asphalt  available  on  the  market  in  1900  and  1903. 

Bermudez  asphalt  is  a  comparatively  pure  bitumen  and  conse- 
quently possesses  the  lustre  of  such  material  instead  of  the  dull 
fracture  of  Trinidad  bitumen  which  is  due  to  the  presence  of 
mineral  matter.  It  has  a  uniform  structure  with  here  and  there 
small  particles  of  vegetable  organic  matter.  The  fracture  at  low 
temperature  is  somewhat  conchoidal  and  the  consistency,  as  shown 
on  the  Bowen  penetration  machine,  ranges  from  22  to  26°.  The 
specific  gravity  of  the  material  is  1.08,  somewhat  higher  than  that 
of  the  pure  bitumen  of  Trinidad  asphalt,  on  account  of  the  presence 
of  a  certain  amount  of  mineral  matter.  The  hydrocarbons  compos- 
ing the  bitumen  consist  to  a  very  considerable  extent  of  such  as 
are  volatile  at  400°  F.,  or  even  at  325°  F.  In  this  respect  it  is 
markedly  different  from  Trinidad  lake  asphalt.  Bermudez  asphalt 
differs  from  Trinidad  lake  asphalt  in  containing  a  larger  percent- 
age of  malthenes,  which  accounts  for  its  greater  softness.  As 
this  percentage  becomes  increased  the  softer  is  the  consistency 
of  the  asphalt,  as  appears  from  the  fact  that  the  softer  refined 
material  of  1903  contains  71.9  per  cent  of  malthenes,  where  that 
of  1900  contained  but  65.4  per  cent. 

The  percentage  of  saturated  hydrocarbons  unacted  upon  by 
sulphuric  acid  in  Bermudez  asphalt  is  about  the  same  as  that 
found  in  Trinidad  lake  asphalt,  so  that  the  bitumens  in  the  two 
asphalts  do  not  differ  essentially  in  this  respect. 

The  undetermined  matter  not  of  a  bituminous  nature  in  Ber- 
mudez is,  as  a  rule,  very  much  smaller  than  in  Trinidad  asphalt  and 


186 


THE  MODERN  ASPHALT  PAVEMENT. 
REFINED  BERMUDEZ  ASPHALT. 


Test  number  

44412 

67753 

Year  

1900 

1903 

PHYSICAL    PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original  sub- 
stance  dry 

1  0823 

1  0575 

Color  of  powder  or  streak  

Black 

Black 

Lustre                       

Bright 

Bright 

Structure          

Uniform 

Uniform 

Fracture       

Semi- 

Semi- 

Hardness,  original  substance  

conchoidal 

Soft 

conchoidal 

Soft 

Odor 

Asphaltic 

Asphaltic 

Softens 

170°  F 

160°  F 

Flows                               

180°  F 

170°  F 

Penetration  at  78°  F  

22° 

26° 

CHEMICAL   CHARACTERISTICS. 

Dry  substance  : 
Loss  325°  F  ,  7  hours     

3  0% 

4  4% 

Character  of  residue   

Smooth 

Smooth 

Loss,  400°  F.,  7  hours  (fresh  sample)  

<8  2% 

9  5% 

Character  of  residue  

Wrinkled 

Shrunken 

Bitumen  soluble  in  CS2,  air  temperature  
Difference               .    .  >  •  

95.0% 
2  5 

96.0% 
2  0 

Inorganic  or  mineral  matter.  

2  5 

2  0 

Malthenes: 
Bitumen  soluble  in  88°  naphtha,  air  tem- 
perature 

100.0 

62  2% 

100.0 
69  1% 

This  is  per  cent  of  total  bitumen  
Per  cent  of  soluble  bitumen  removed  by 
H,SO4 

65.4 
62  4 

71.9 
67  4 

Per  cent  of  total  bitumen  as  saturated  hy- 
drocarbons 

24  4 

23  4 

Bitumen  soluble  in  62°  naphtha  

69.2% 

75.9% 

This  is  per  cent  of  total  bitumen 

72  8 

79  0 

Carbenes  : 
Per    cent    bitumen    insoluble    in    carbon 
tetrachloride,  air  temperature  

0.1% 

1.1% 

Bitumen  yields  on  ignition:  " 
Fixed  carbon  

13.4% 

14.0% 

Sulphur  

4  0% 

INDIVIDUAL  ASPHALTS. 


187 


EXTREMES   IN  THE   COMPOSITION   OF   REFINED   BERMUDEZ 

ASPHALT. 


PHYSICAL    PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original  substance, 
dry       

1.085 

1.057 

Flow  in  per  cent  of  average 

41.6% 

178% 

CHEMICAL    CHARACTERISTICS. 

Dry  substance: 
Loss  325°  F    7  hours            

5.5% 

1.5% 

Loss  400°  F    7  hours  (fresh  sample) 

9  5% 

4  5% 

Bitumen  soluble  in  CS    air  temperature  

93.0% 

96.8% 

Difference             

5.0 

1.4 

2.0 

1.8 

Malthenes: 
Per  cent  total  bitumen  soluble  in  88°  naphtha, 
air  temperature                     

100.0 
65.0 

100.0 
73.0 

Per  cent  total  bitumen  soluble  in  62°  naphtha.  . 

Bitumen  yields  on  ignition  : 
Fixed  carbon 

72.0 
14.0 

83.0 
13.5 

of  an  entirely  different  origin.  In  Bermudez  asphalt  it  is  derived 
almost  entirely  from  vegetable  organic  matter  in  the  shape  of  grasses 
and  twigs  with  which  the  pitch  has  become  contaminated.  As  a 
result  of  this,  when  the  asphalt  is  made  into  a  cement  with  a  flux 
and  maintained  in  a  melted  condition  for  a  considerable  period 
of  time,  this  settles  out  on  the  bottom  of  the  melting-tank  as  the 
gummy  material  which  has  been  mentioned  by  the  persons  not 
further  investigating  its  nature.  If  this  gummy  material  is 
extracted  with  carbon  disulphide,  the  vegetable  nature  of  the 
material  will  be  revealed  at  once. 

If  the  ultimate  composition  of  the  bitumen  of  Bermudez  asphalt 
where  it  exudes  into  the  lake  and  that  of  the  pure  Trinidad  bitu- 
men are  compared,  it  will  be  noticed  that  they  agree  very  closely 
in  their  composition  (see  table,  page  188). 

The  percentage  of  fixed  carbon  which  Bermudez  refined  asphalt 
yields  on  ignition  is  much  higher  than  that  found  in  Trinidad 


188 


THE  MODERN  ASPHALT  PAVEMENT 


COMPARISON  OF  ULTIMATE  COMPOSITION  OF  PURE  BITUMEN, 
BERMUDEZ  AND  TRINIDAD  ASPHALT. 


Bermudez, 
Pure  Bitumen. 

Trinidad, 
Pure  Bitumen. 

Carbon     

82  88% 

82  33% 

Hydrogen  

10  79 

10  69 

Sulphur  

5.87 

6  16 

Nitrogen  

.75 

81 

100.29 

99.99 

asphalt  and  it  is  an  amount  which  is  usually  characteristic  of  all 
the  native  bitumens  which  are  distinctly  asphaltic  in  their  nature. 

The  amount  of  sulphur  is  greater  in  the  softer  than  hi  the 
harder  varieties. 

From  the  preceding  data  the  two  most  important  asphalts 
in  use  in  the  paving  industry  may  be  compared  with  the  following 
results: 

Trinidad  asphalt  is  one  which  carries  a  very  considerable  amount 
of  mineral  matter  which  acts  as  a  filler.  Bermudez  asphalt  is  a 
nearly  pure  bitumen.  Trinidad  asphalt  is  very  stable  at  high 
temperatures  and  but  little  susceptible  to  change.  Bermudez 
asphalt  volatilizes  an  appreciable  amount  of  light  oils  at  high 
temperatures  and  hardens  very  rapidly.  Bermudez  asphalt  con- 
tains a  larger  percentage  of  malthenes  than  Trinidad  and  on  this 
account  is  more  susceptible  to  temperature  changes.  Finally, 
Trinidad  asphalt  is  a  substance  of  fixed  and  extremely  uniform 
composition,  while  Bermudez  asphalt  is  most  variable  in  this  re- 
spect, material  from  different  parts  of  the  deposit  showing  great  lack 
of  uniformity  in  both  its  physical  and  chemical  properties.  The 
relative  merits  of  the  two  materials  from  an  industrial  point  of  view 
will  be  considered  later  when  surface  mixtures  are  under  discussion. 

Maracaibo  Asphalt. — The  asphalt  used  in  the  paving  industry, 
known  as  Maracaibo  asphalt,  is  put  upon  the  market  by  the  United 
States  and  Venezuela  Company.  It  is  found  in  the  State  of  Zulia, 
west  of  the  Gulf  of  Maracaibo,  on  the  river  Limon,  about  50  miles 
west  from  the  City  of  Maracaibo,  as  shown  on  the  accompanying 
map,  Fig.  5.  The  principal  deposit  is  known  as  that  of  Inciarte. 


INDIVIDUAL  ASPHALTS. 


189 


It  is  an  exudation,  from  maltha  springs,  of 
gathered  up  and  crudely  refined,  after  which 
the  river  to  the  village  of  Toas,  at  the  opening 
into  the  Gulf,  from  which  point  it  is  shipped  to 
The  material  resembles  and  possesses  many 
tics  of  the  crude  Bermudez  asphalt,  but  it  is 


bitumen  which  is 
it  is  floated  down 
of  Maracaibo  Lake 
the  United  States, 
of  the  characteris- 
distinguished  from 


eflnery^  __ 

Maracaibo 
LaPaz  Deposit 
STAT.E   OF   ZULIA 

V        E        N       yJE  Z 

MAMA  CALBO 


FlG.  5. 

it  by  having  a  markedly  rank  odor  suggestive  of  unsaturated 
hydrocarbons  and  of  sulphur  derivatives.  This  odor  may,  how- 
ever, be  due  somewhat  to  cracking  which  has  taken  place  during 
refining,  since  in  the  analysis  of  the  material  numbered  66923 
seventeen  per  cent  of  the  bitumen  is  in  the  form  of  carbenes 
insoluble  in  cold  carbon  tetrachloride,  while  in  the  samples  col- 
lected in  1904  less  than  two  per  cent  is  in  this  form. 

Five  analyses  of  the  crudely  refined  material  made  itt.  th 
York  Testing  Laboratory  have  resulted  as  follows: 


190 


THE  MODERN  ASPHALT  PAVEMENT. 


MARACAIBO 


Test  number 60380 

Date  sample  received 6-19-02 

PHYSICAL   PROPERTIES. 

Specific  gravity,  78°  F./780 F.,  original  substance,  dry 1 .0784 

Color  of  powder  or  streak Black 

Lustre Bright 

Structure Uniform- 

homogeneoui 

Fracture Semi- 

conchoidal 

Hardness,  original  substance 1 

Odor Strong 

Softens 280°  F. 

Flows 300°  F. 

Penetration  at  78°  F 8° 

CHEMICAL   CHARACTERISTICS. 

Original  substance : 

Loss,  212°  F.,  1  hour Trace 

Dry  substance : 

Loss,  325°  F.,  7  hours S.3%1 

Character  of  residue .... 

Loss,  400°  F.,  7  hours  (fresh  sample) 

Character  of  residue .... 

Bitumen  soluble  in  CS2,  air  temperature 92 . 2% 

Difference 6.3 

Inorganic  or  mineral  matter 1.5 

100.0 

Malthenes : 

Bitumen  soluble  in  88°  naphtha,  air  temperature 45 . 8% 

This  is  per  cent  of  total  bitumen 49 . 7 

Per  cent  of  soluble  bitumen  removed  by  H2SO4 .... 

Per  cent  of  total  bitumen  as  saturated  hydrocarbons .... 

Bitumen  soluble  in  62°  naphtha 49. 7% 

This  is  per  cent  of  total  bitumen 53 . 5 

Carbenes : 

Bitumen  insoluble  in  carbon  tetrachloride,  air  temperature.  .... 

Bitumen  yields  on  ignition: 

Fixed  carbon ^ 19.0% 

Vegetable  organic  matter .... 


1  Loss  determined  in  open  dish  temperature  325°  to  350°  F. 


INDIVIDUAL  ASPHALTS. 


191 


ASPHALT. 


61047 

66923 

72214 

72215 

8-20-02 

10-19-03 

8-25-04 

8-25-04 

1.0634 
Black 
Bright 
Uniform 

1.0638 
Black 
Bright 
Uniform 

1.0660 
Black 
Bright 
Uniform 

1.0621 
Black 
Bright 
Uniform 

Semi- 
conchoidal 
Soft 
Strong 
220°  F. 
230°  F. 
25° 

Semi- 
conchoidal 
Soft 
Strong 
200°  F. 
210°  F. 
20° 

Semi- 
conchoidal 
Soft 
Strong 
215°  F. 
230°  F. 
27° 

Semi- 
conchoidal 
Soft 
Strong 
195°  F. 
210°  F. 
26° 

Trace 

•  3% 

4.5%' 

2.7% 
Blistered 

1.5% 
Smooth 

1.5% 
Smooth 

.":::.:      : 

4-7% 
Much  blistered 

5.8% 
Blistered 

6.0% 
Blistered 

94.0% 
4.5% 
1.5 

96.8% 
1.4 
1.8 

92.2% 
2.0 
5.8 

94.3% 
2.1 
3.6 

100.0 

100.0 

100.0 

100.0 

54.5% 
57.9 

45.7% 
47.2 
46.4 
25.3 

53.4% 
57.9 
48.5 
25.5 

53.9% 
57.2 
49.2 
29.1 

59.5% 
63.3 

51.5% 
53.2 

A 



17.  5%  2 

1.5% 

1.3% 

15.0% 

18.0% 

17.0% 

16.9% 



8.0% 

2  Duplicate  17.8%. 


192  THE  MODERN  ASPHALT  PAVEMENT. 

It  appears  from  the  preceding  data  that  Maracaibo  asphalt, 
like  that  from  the  Bermudez  lake,  contains  considerable  vegetable 
organic  matter.  On  re-refining  in  the  laboratory  it  has  a  density 
corresponding  to  the  pure  bitumen  of  Trinidad  lake  asphalt,  that 
is  to  say,  somewhat  less  than  that  of  Bermudez,  and  a  very  con- 
siderable degree  of  purity,  from  92  to  97  per  cent.  The  refined 
material  is  soft  enough  to  be  indented  with  the  finger-nail.  Apart 
from  the  preceding  characteristics  it  differs  in  other  respects  from 
Bermudez  asphalt  and  from  other  asphalts  with  which  we  are 
acquainted.  Its  softening-point  is  not  only  higher  than  that  of 
Bermudez  asphalt  but  even  that  of  Trinidad.  It  contains  a  very 
small  percentage  of  malthenes,  which  might  be  expected  from  its 
high  softening-point,  but  not  from  its  consistency.  The  percent- 
age of  saturated  hydrocarbons  found  in  the  malthenes  is  25  to 
29  per  cent.  The  percentage  of  fixed  carbon  obtained  on  ignition 
is  higher  than  that  found  in  the  normal  asphalts,  reaching  18  per 
cent.  On  heating  it  to  a  temperature  not  above  325°  F.  gas  is 
evolved  showing  that  the  bitumen  is  unstable  and  in  a  state  of 
change.  What  effect  these  peculiarities  may  produce  in  the 
asphalt  pavements  constructed  with  it  time  and  experience  alone 
can  tell. 

Cuban  Asphalts. — Many  different  forms  of  native  bitumens  are 
found  in  the  island  of  Cuba  but  the  deposits  are  of  such  small 
extent  in  any  one  place  that  they  are  of  no  great  commercial  inter- 
est, except  that  they  are  imported  in  small  amounts  for  the  manu- 
facture of  varnishes  and  in  one  or  two  instances  for  paving  purposes. 
Solid  bitumen,  in  the  form  of  grahamite,  has  been  mined  in 
the  Provinces  of  Pinar  del  Rio  and  Havana,  but  no  attempts  have 
been  made  to  utilize  these  in  the  paving  industry.  In  the  neigh- 
borhood of  the  village  of  Bejucal,  18  miles  south  of  Havana,  there 
are  several  mines  of  bitumen  of  an  asphaltic  nature,  one  of  which 
has  been  worked  on  a  commercial  scale  and  utilized  in  the  United 
States  in  the  construction  of  pavements  in  Washington,  D.  C.  The 
bitumen  is  more  or  less  variable.  A  specimen  of  it  had  the  follow- 
ing composition: 


INDIVIDUAL  ASPHALTS. 


193 


ASPHALT  FROM  BEJUCAL  DISTRICT,  CUBA. 

Test  number 22220 

PHYSICAL   PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original  substance,  dry 1 .305 

Color  of  powder  or  streak Red-brown 

Lustre Dull 

Structure Compact 

Fracture Semi-conchoidal 

Hardness 2 

Odor Asphaltic 

Softens 230°  F 

Flows 240°  F 

Penetration  at  78°  F 0° 

CHEMICAL   CHARACTERISTICS. 

Dry  substance: 

Loss,  325°  F.,  7  hours .88% 

Character  of  residue Cracked 

Loss,  400°  F.,  7  hours  (fresh  sample) 1 .50% 

Character  of  residue Wrinkled 

Bitumen  soluble  in  CS2,  air  temperature 75. 1% 

Difference 3.5 

Inorganic  or  mineral  matter 21.4 

100.0 

Malthenes: 

Bitumen  soluble  in  88°  naphtha,  air  temperature 32 . 4% 

This  is  per  cent  of  total  bitumen 43 . 1 

Per  cent  of  soluble  bitumen  removed  by  H.5SO4 60 . 5 

Per  cent  of  total  bitumen  as  saturated  hydrocarbons 17.0 

Bitumen  soluble  in  62°  naphtha 39.6% 

This  is  per  cent  of  total  bitumen 52 . 7 

Carbenes : 

Bitumen  more  soluble  in  carbon  tetrachloride,  air  temper- 
ature   1.6% 

Bitumen  yields  on  ignition: 

Fixed  carbon 25.0% 

Sulphur 8.3% 


194  THE  MODERN  ASPHALT  PAVEMENT. 

In  general  appearance  the  Bejucal  asphalt  resembles  the  Trini- 
dad refined  material.  It  contains  about  21  per  cent  of  mineral 
matter  in  the  form  of  silica  and  silicates  and  75  per  cent  of  bitumen. 
The  specific  gravity  of  the  asphalt  corresponds  to  a  mixture  of 
bitumen  and  mineral  matter  in  these  proportions.  It  has  a  very 
high  softening  point.  The  percentage  of  its  total  bitumen  in  the 
form  of  saturated  hydrocarbons  as  revealed  by  the  action  of  sul- 
phuric acid  on  the  malthenes  soluble  in  88°  naphtha  is  smaller 
than  that  in  Trinidad  asphalt.  It  contains  a  large  percentage 
of  sulphur  and  yields  a  high  percentage  of  fixed  carbon,  larger 
than  that  usually  found  in  any  of  the  asphalts.  In  this  respect 
it  is  more  closely  allied  to  the  grahamites  than  to  the  asphalts, 
and  it  may  perhaps  eventually  be  necessary  to  classify  it  with 
the  latter  form  of  bitumen.  As  might  be  expected  from  its 
extreme  hardness,  the  percentage  of  malthenes  is  only  about  two- 
thirds  as  much  as  that  found  in  Trinidad  and  Bermudez  asphalt, 
and  this  necessitates  the  use  of  a  heavy  asphaltic  flux  in  the  prepa- 
ration of  a  satisfactory  asphalt  cement  from  this  material. 

In  the  neighborhood  of  the  Bejucal  mine  are  several  others, 
partial  examinations  of  which  have  been  made  giving  the  results 
tabulated  on  page  '195. 

Mexican  Asphalt. — Native  bitumen  in  the  shape  of  maltha 
and  in  a  more  or  less  solid  form  is  of  frequent  occurrence  in  Mexico, 
especially  along  the  coast  of  the  Gulf  of  Mexico,  in  the  States  of 
Tamaulipas  and  Vera  Cruz.  In  the  neighborhood  of  Tampico 
and  Tuxpan  attempts  have  been  made  for  many  years  to  work 
the  large  effusions  of  maltha  which  occur  there.  At  none  of  these 
deposits,  however,  is  there  a  sufficient  amount  of  bitumen  avail- 
able to  make  the  material  of  commercial  importance.  Lots  of 
several  hundred  tons  have,  however,  been  collected  and  shipped 
to  the  United  States  and  used  in  pavements,  so  that  it  may  be 
a  matter  of  interest  to  determine  what  the  character  of  the  bitu- 
men is. 

Asphalt  Effusions  on  the  Tamesi  River. — At  about  45  miles  from 
Tampico  and  25  miles  from  Los  Esteros,  a  station  on  the  Me. 
&  Gulf  R.R.,  there  are  large  tar  springs.  From  these  effusions 
some  hundreds  of  tons  of  asphalt  have  been  collected  from  time 


INDIVIDUAL  ASPHALTS. 


195 


DEPOSITS   IN   THE   NEIGHBORHOOD   OF   THE   BEJUCAL 
MINE,   CUBA. 


Test  number                                          

22221 

Name  of  mine  

"Angelo 

"Raboul" 

PHYSICAL   PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original  sub- 
stance dry                                    

Elmira" 
1  348 

1.306 

Color  of  powder  or  streak  

Dark  brown 

Brown 

Lustre                 

None 

None 

•  Uniform 

Brecciated 

Semi- 

Conchoidal 

Hardness  original  substance.  .               

conchoidal 
3 

2 

Softens                                            

245°  F. 

240°  F. 

Flows                                 

270°  F. 

250°  P. 

Penetration  at  78°  F  

0° 

0° 

CHEMICAL   CHARACTERISTICS. 

Original  substance: 
Loss,  212°  F  ,  1  hour  

3.2% 

.4% 

Bitumen  soluble  in  CS2  air  temperature 

68  6% 

73  0% 

Difference    ...        ....                   .    . 

3  5 

4  0 

Inorganic  or  mineral  matter   

27  9 

23  0 

Malthenes: 
Per  cent  of  total  bitumen  soluble  in  88° 
naphtha  air  temperature 

100.0 
36  6% 

100.0 
49  3% 

Per  cent  of  total  bitumen  soluble  in  62° 

64.5% 

Carbenes: 
Bitumen  insoluble  in  carbon  tetrachloride, 
air  temperature  

14.3% 

Bitumen  yields  on  ignition: 
Fixed  carbon  

17  4% 

to  time  and  shipped  to  the  United  States.  The  material  is  not  ot 
uniform  composition,  samples  collected  in  1899  and  examined  in 
the  author's  laboratory  having  the  characteristics  given  in  the  first 
table  on  page  196  and  in  the  table  on  page  197. 

It  appears  that  this  bitumen  although  usually  originally  quite 
hard,  as  shown  by  the  penetration  at  78°  F.,  loses  a  large  amount 
of  volatile  matter  on  heating  and  becomes  converted  into  a  pitch 


196 


THE  MODERN  ASPHALT  PAVEMENT. 


FROM  TAMESI  RIVER,  MEXICO. 

SAMPLES    COLLECTED    AT   DEPOSIT. 


Test  number           

28075 

28076 

28077 

28078 

Bitumen  soluble  in  CSa,  air  temp  .  . 
Difference  .  .        

99.5% 
0.0 

68.3% 
6.8 

59.7% 
6.9 

68.1% 

Inorganic  or  mineral  matter 

5 

24  9 

33  4 

29  5 

Loss,  230°  F.,  until  dry  
Loss,  325°  F.,  7  hours  additional.  . 
Loss,  400°  F.,  5  hours  additional.  . 

2.83% 
17.30 
8.42 

13.50% 
7.46 
3.36 

4.37% 
6.34 
2.42 

9.66% 
13.75 
9.68 

Residue  after  325°  and  400°  

Pitch 

Pitch 

Pitch 

Pitch 

Penetration  of  original  material 
at  78°  F  

25° 

40° 

25° 

57° 

in  all  cases.  The  instability  of  the  material,  as  revealed  by  this 
fact,  would  necessitate  the  heating  of  this  bitumen  until  all  the 
volatile  portion  was  removed  before  it  could  be  used  for  paving 
purposes  satisfactorily.  For  this  reason,  as  well  as  on  account 
of  its  great  lack  of  uniformity  and  the  small  extent  of  the  avail- 
able supply,  it  will  not,  probably,  play  a  very  important  part  in 
the  asphalt  paving  industry. 

Deposits  at  Chijol. — At  a  locality  known  as  Chijol,  25  miles 
from  Tampico,  on  the  Mex.  Cent.  R.R.,  and  3  miles  distant  from 
the  latter,  asphalt  effusions  have  been  worked  to  a  limited  extent. 
A  sample  of  this  material  has  the  following  characteristics: 

TEST  NO.  28082. 

Loss,  250°  F.,  until  dry 12.70% 

Penetration  at  78°  F.  (original  substance) 66° 

DRY   SUBSTANCE. 

Loss,  325°  F.,  7  hours 13.42% 

Residue  after  heating Pitch 

Loss,  400°  F.,  5  hours 7.24% 

Residue  after  heating Pitch 

Bitumen  soluble  in  CS2,  air  temperature. ...       91 . 1% 

Difference 1.7 

Inorganic  or  mineral  matter  7.2 


100.0 


INDIVIDUAL  ASPHALTS. 


197 


FROM  TAMESI  RIVER,  MEXICO. 

SAMPLES   SHIPPED   TO   NEW   YORK. 


44312 

51471 

51470 

Specific  gravity,  78°  F  /78°  F   (original) 

1  211 

1  0385 

*"  '  '             '  '                 "         (dry)  °  ...'.. 

1  118 

Flashes,  °F  

308°  F 

Loss,  212°  F.,  until  dry  

15.0% 

20.1% 

10  0% 

Loss  on  refining  —  water           

15  o% 

20  1% 

1  '     "        '  '      —  impurities  

8  0 

22  2 

Total  loss  

23  0 

42  3% 

Penetration  of  refined  substance  at  78°  F.  .  . 

REFINED    SUBSTANCE. 

Loss,  325°  F.,  7  hours    .                    

16° 

1  5% 

38° 

1  8% 

4  8% 

Penetration  of  residue  at  78°  F  

15° 

70° 

Loss,  400°  F.,  7  hours  (fresh  sample)  

4  3% 

5  5% 

8  9% 

Penetration  of  residue  at  78°  F  

Pitch 

Pitch 

50° 

Loss,  325°  F.,  21  hours.  . 

3  4% 

«              it              no          «  < 

10  4% 

Loss,  400°  F  ,  21  hours  . 

7  4% 

"           "       28     "       

16  9% 

Bitumen  soluble  in  CSa,  air  temperature  .... 
T^ifference                       ... 

89.1% 
1  8 

71.5% 
8  3 

99.0% 

Inorganic  or  mineral  matter     

9  1 

20  2 

5 

Mai  t  henes  : 
Bitumen    soluble    in    88°    naphtha,    air 
temperature 

100.0 
49  5% 

100.0 

48  8% 

100.0 
73  9<£ 

This  is  per  cent  of  total  bitumen  soluble.  . 
Bitumen  soluble  in  62°  naphtha     

55.6 
57  0% 

68.2 
56  2% 

74.6 
83  8% 

This  is  per  cent  of  total  bitumen  soluble.  . 

Bitumen  yields  on  ignition: 
Fixed  carbon                            

64.0 
16  1% 

78.7 
10  4% 

84.6 
12  6% 

It  will  be  noted  that  this  bitumen  is  very  similar  to  the  purer 
form  of  that  found  along  the  Tamesi  River;  that  is  to  say,  it  loses 
large  quantities  of  volatile  matter  on  heating  and  becomes  con- 
verted into  a  pitch.  For  the  same  reasons,  as  in  the  case  of  the 
previous  bitumen,  it  will  not  prove  of  any  importance  in  the  paving 


198  THE  MODERN  ASPHALT  PAVEMENT. 

industry,  although  no  doubt  a  certain  proportion  of  both  of  these 
materials  could  be  incorporated  with  other  and  more  satisfactory 
asphalts  if  it  were  a  matter  of  economy  to  do  so. 

Deposits  in  the  Neighborhood  of  Tuxpan. — 54  miles  from  Tuxpan 
and  9  miles  from  the  Tuxpan  River  are  found  large  effusions  of 
asphalt,  identified  under  the  name  of  the  Santa  Theresa  deposits, 
attempts  to  develop  which  have  been  made  for  many  years,  and 
by  many  individuals,  and  with  but  little  success  from  a  com- 
mercial point  of  view. 

A  sample  of  the  material  examined  in  the  author's  laboratory 
had  the  following  characteristics: 

FROM  DEPOSIT  AT  TUXPAN,  MEXICO. 

TEST  No.  28083. 
Loss,  230°  F.,  until  dry 15.30% 

Penetration  at  78°  F.  (original  substance)  —         76° 

DRY   SUBSTANCE. 

Loss,  325°  F.,  7  hours 12.48% 

Residue  after  heating Pitch 

Loss,  400°  F.,  5  hours  additional 6 . 84% 

Residue  after  heating Pitch 

Bitumen  soluble  in  CS2,  air  temperature ...     90 . 3% 

Difference 3.1 

Inorganic  or  mineral  matter 6.6 

100.0 

This  bitumen  is,  it  will  be  seen,  quite  similar  to  those  found 
near  Tampico. 

Deposits  at  Chapapote. — Effusions  of  asphalt  which  are  iden- 
tified under  the  above  name  occur  15  miles  from  Timberdar,  the 
head  of  navigation  of  the  Tuxpan  River.  These  deposits  have 
been  worked  by  the  Mexcian  Asphalt  Company,  who  packed  the 
material  in  bags  and  made  an  effort  to  float  it  down  the  river. 
Some  of  the  bitumen  thus  exported  was  examined  by  the  author, 
giving  the  results  tabulated  on  page  199. 

From  these  data  it  appears  that  both  soft  and  hard  bitu- 
men are  found  on  the  Chapapote  Ranch,  but  that  the  former 
hardens  very  rapidly  on  heating,  like  other  Mexican  bitumens, 


INDIVIDUAL  ASPHALTS. 
FROM  DEPOSIT  AT  CHAPAPOTE,  MEXICO. 


199 


42226 

28080 

Specific  gravity  at  78°  F./780  F.  (original)  .  , 

1  0343 

'    "        "             "             (dry).. 

1.045 

Color  

Black 

Lustre                                                •    . 

Shining 

Structure                           .    .          

Massive 

Fracture            

Conchoidal 

2  + 

Readily 

Softens                                                  .            .... 

258°  F 

Flows.                                        

272°  F 

Penetration  at  78°  F.  (dry)  

140° 

Loss,  220°  F.,  2  hours  

11.4% 

DRY   SUBSTANCE. 

Loss  325°  F  ,  7  hours                    .    .           

4  7% 

Residue  after  heating,  penetration  at  78°  F  

84° 

Loss  400°  F    7  hours  (fresh  sample) 

13  0% 

Residue  after  heating,  penetration  at  78°  F. 

32° 

Bitumen  soluble  in  CS2^  air  temperature  

99  0% 

99  2% 

.4 

Inorganic  or  mineral  matter.        .  .  . 

6 

7 

Malthenes  : 
Bitumen  soluble  in  88°  napntha,  air  temperature 
This  is  per  cent  of  total  bitumen 

100.0 

74.1% 
74  8 

100.0 

Bitumen  soluble  in  62°  naphtha  . 

83  5% 

This  is  per  cent  of  total  bitumen   

84  3 

Bitumen  yields  on  ignition  : 
Fixed  carbon  

13  3% 

21  5% 

and  becomes  converted  into  a  pitch.  The  material  of  this  descrip- 
tion which  has  been  imported  into  the  United  States  has  been 
used  by  mixing  it  with  other  more  desirable  asphalts,  or,  where 
used  alone,  has  made  a  more  or  less  unsatisfactory  pavement. 

Malthas  and  solid  bitumens  from  various  other  deposits  in 
Mexico  have  been  examined  in  the  author's  laboratory  but  the 
preceding  are  sufficient  to  illustrate  the  general  character  of  the 
material  found  in  that  country.  From  information  available  it 
hardly  seems  possible  that  any  of  these  deposits  can  ever  furnish 


200  THE  MODERN  ASPHALT  PAVEMENT. 

a  reliable  commercial  supply.  They  have  been  mentioned  in  this 
place  merely  to  bring  out  this  fact  and  to  show  the  character  of 
the  material  that  is  available. 

La  Patera,  California,  Asphalt. — In  Santa  Barbara  County,  Cali- 
fornia, and  about  9J  miles  in  an  air-line  west  of  the  City  of  Santa 
Barbara,  a  vein  or  intrusion  of  asphalt  in  the  shales  of  that  neigh- 
borhood was  worked  for  several  years  in  the  early  nineties.  Its 
geologic  environment  has  been  described  by  Eldridge.1 
The  material  was  used  in  the  production  of  an  asphalt  cement  which 
attracted  much  attention  at  that  time,  and  was  known  as  Alca- 
traz  XX.  Although  the  vein  is  now  exhausted  and  the  mine 
abandoned  the  bitumen  is  of  some  interest  as  being  typical  and 
illustrative  of  the  hardest  type  of  asphalt.  In  its  best  days  it 
never  yielded  more  than  70  tons  in  a  day  and  generally  not  more 
than  30  or  40,  the  entire  production  in  the  5  years  that  it  was 
worked  being  less  than  30,000  tons. 

La  Patera  crude  asphalt  is  a  mixture  of  bitumen  with  the  min- 
eral matter  of  the  adjoining  shale,  which  is  composed  of  sand 
and  clay.  Its  fracture  resembles  in  some  respects  Trinidad  lake 
asphalt,  the  material  being  filled  with  small  gas  cavities  due  to 
the  imprisonment  of  gas  which  has  been  evolved  at  an  early  stage 
in  the  existence  of  the  material  in  the  same  way  that  takes  place 
in  Trinidad  pitch.  It  differs  from  the  latter  in  being  very  hard 
and  brittle,  not  softening  below  250°  F.  Material  taken  from 
the  mine  in  1894  contained  59  per  cent  of  bitumen  but  in  1896 
this  fell  to  55  per  cent  and  in  1897  it  had  fallen  to  49  per  cent. 
The  latter  material  had  the  physical  properties  and  proximate 
composition  given  in  the  table  on  page  201. 

From  these  figures  it  appears  that  the  density  corresponds  to 
the  percentage  of  mineral  matter  and  bitumen  which  it  contains. 
As  has  already  been  said,  the  softening  point  is  very  high.  It  of 
course,  being  so  hard  a  material,  loses  but  little  on  heating  for  a 
length  of  time  at  high  temperature.  The  percentage  of  malthenes 
is,  of  course,  very  low  and  corresponds  to  that  found  in  the  Cuban 
asphalt.  The  percentage  of  hydrocarbons  unacted  on  by  sulphuric 
acid  is  low,  lower  even  than  in  the  Bejucal,  Cuban,  bitumen,  and 
1  The  Asphalt  and  Bituminous  Rock  Deposits  of  the  U.  S.,  1901,  442. 


INDIVIDUAL  ASPHALTS.  201 

LA  PATERA,  CALIFORNIA,  ASPHALT. 

Test  number 13541 

PHYSICAL   PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original  substance,  dry 1 . 3808 

Color  of  powder  or  streak Black 

Lustre Dull 

Structure Uniform 

Fracture   Irregular 

Hardness,  original  substance 2 

Odor Asphalti* 

Softens 260°  P 

Flows 300°  P 

Penetration  at  78°  F 0° 

CHEMICAL    CHARACTERISTICS. 

Dry  substance : 

Loss,  325°  F.,  7  hours 1.5% 

Character  of  residue , Shrunke* 

Loss,  400°  F.,  7  hours  (fresh  sample) 2.5% 

Character  of  residue Shrunken 

Bitumen  soluble  in  CSa,  air  temperature 49.3% 

Difference 2.1 

Inorganic  or  mineral  matter 48.6 

100.0 

Malthenes: 

Bitumen  soluble  in  88°  naphtha,  air  temperature 21 .6% 

This  is  per  cent  of  total  bitumen 43 . 8 

Per  cent  of  soluble  bitumen  removed  by  H^Oj 81 . 4 

Per  cent  of  total  bitumen  as  saturated  hydrocarbons 8.1 

Bitumen  soluble  in  62°  naphtha 26.7% 

This  is  per  cent  of  total  bitumen 54 . 1 

Carbenes: 

Bitumen  more  soluble  in  carbon  tetrachloride,  air  temperature  1 . 7% 

Bitumen  yields  on  ignition : 

Fixed  carbon 14.9% 

Sulphur 6.2% 

the  lowest  found  in  any  asphalt.     It  yields  about  15  per  cent  of 
fixed  carbon  on  ignition  and  is,  therefore,  a  true  asphalt  and  in  no 


202  THE  MODERN  ASPHALT  PAVEMENT. 

way  allied  to  the  grahamites.  The  percentage  of  sulphur  which 
it  contains  is  the  same  as  that  found  in  Trinidad  asphalt. 

An  asphalt  of  this  description  can  only  be  used  in  combination 
with  a  dense  residuum  of  an  asphaltic  petroleum.  In  the  early 
days  of  the  Alcatraz  Company  attempts  were  made  to  produce  a 
paving  cement  by  combining  La  Patera  asphalt  with  the  natural 
maltha  found  in  the  Carpinteria  sands.  Pavements  made  with 
this  material  went  to  pieces  very  rapidly,  and  it  is  not  difficult, 
in  the  light  of  our  present  knowledge,  to  explain  why  this  was  so. 
The  Carpinteria  maltha  hardens  and  becomes  a  pitch  very  rapidly 
on  heating,  with  the  result  that  it  is  impossible  to  guarantee  that 
an  asphalt  cement  made  with  it  should  have  a  proper  consistency 
in  an  asphalt  surface.  Later  on  a  heavy  asphaltic  petroleum 
residuum  obtained  from  a  petroleum  produced  at  Summerland 
was  used  with  much  more  satisfactory  results,  and  some  excellent 
pavements  were  laid  with  a  cement  prepared  in  this  way,  but 
the  proportion  of  the  La  Patera  asphalt  to  the  oil,  40  to  60,  was 
so  small  that  it  could  be  better  regarded  as  an  amendment  to 
qualities  lacking  in  the  oil  rather  than  as  an  asphaltic  cement  per  se. 

Asphalt  on  the  More  Ranch,  Santa  Barbara  County,  California. 
— This  deposit  of  asphalt  is  of  importance  not  on  account  of  its  size, 
but  because  the  addition  of  perhaps  a  shovelful  of  it  to  each  barrel 
of  residual  pitch  from  California  petroleum  has  been  used  as  a 
basis  for  the  statement  that  the  latter  contains  a  native  solid 
bitumen.  The  deposit  is  found  on  the  seashore  about  6  miles 
to  the  west  of  Santa  Barbara.  It  has  been  described  by  Mr.  J.  D. 
Whitney  in  his  report  on  the  Geological  Survey  of  California, 
Geology,  I,  132,  by  Peckham  in  the  American  Jour,  of  Science, 
(2),  48,  368,  and  by  Eldridge. 

The  shore  here  consists  of  an  exposed  cliff,  75  to  80  feet  high, 
of  sandy  clay  which  is  quite  soft  and  easily  weathered.  It  is 
much  fissured  and  in  these  fissures  the  asphalt  is  found  either 
in  the  shape  of  kidneys  or  veins.  It  can  be  seen  at  various  points 
along  the  face  of  the  cliff,  where  it  has  been  exposed  by  the  action 
of  the  waves.  In  places  the  wall  rock  is  mixed  in  in  fragments 
with  the  bitumen  and  in  others  it  is  a  homogeneous  material. 
The  amount  of  bitumen  found  at  any  point  is,  therefore,  very 


INDIVIDUAL  ASPHALTS. 


203 


variable,  as  can  be  seen  from  the  accompanying  analyses.  A  few 
hundred  tons  have  been  taken  out  annually  for  many  years  and 
sold  along  the  Pacific  Coast.  When  the  author  examined  the 
deposit  in  1897  a  kidney  was  being  worked  about  15  feet  deep 
and  about  12  feet  broad,  which  illustrated  the  appearances  of  the 
material;  larger  masses  than  this  are  seldom  found.  It  is  evi- 
dent, therefore,  that  the  asphalt  available  at  this  point  is  not  of 
commercial  importance.  The  composition  of  the  material  is  as 
follows: 

ANALYSES  OF  ASPHALT  FROM  MORE  RANCH,  SANTA 
BARBARA  COUNTY,  CALIFORNIA. 

Test  No.  13383.  From  mine,  collected  December,  1897. 
"     "     13536.  Supply  ready  for  shipment  on  wharf. 
"     "     13539.  Stringer  in  tunnel  from  pit. 


DRY   SUBSTANCE. 

13383 

13536 

13539 

Bitumen  by  CS2  air  temperature   .  .  . 

38  3% 

40  1% 

48  ^^ 

3.4 

1.4 

*0  .  O  /0 

1  2 

58  3 

58  5 

50  5 

Malthenes  : 
Per  cent  of  total  bitumen  soluble  in  88° 
naphtha  air  temperature     

100.0 
63  2 

100.0 
63  3 

100.0 
59  2 

Loss  of  crude  at  212°  F.,  1  hour  

•7% 

1.4% 

1.4% 

It  is  evident  that  the  asphalt  contains  too  little  bitumen  to 
melt  readily  without  the  aid  of  a  flux.  The  pure  bitumen  extracted 
from  the  asphalt  is  much  harder  than  that  obtained  from  Trinidad 
lake  asphalt,  flowing  but  69  per  cent  as  far  as  the  latter  on  a  cor- 
rugated plate  at  high  temperature. 

All  attempts  to' utilize  this  material,  except  locally,  have  been 
made  purely  for  advertising  purposes  in  connection  with  the  use 
of  residual  pitches,  where  specifications  demanded  the  use  of  a 
native  solid  bitumen. 

Standard  Asphalt. — In  the  western  part  of  Kern  County,  in 
the  first  tier  of  foot-hills  on  the  coast  range,  forming  the  western 
boundary  of  the  central  valley  of  California,  at  a  point  called 


204 


THE  MODERN  ASPHALT   PAVEMENT. 


Asphalto,  at  the  end  of  a  branch  of  the  Southern  Pacific  Railroad 
from  Bakersfield,  an  asphalt  mine  was  in  existence  in  the  nineties 
which  was  worked  by  the  Standard  Asphalt  Company  of  Cali- 
fornia. The  company  originally  endeavored  to  work  certain 
superficial  overflows  of  bitumen  upon  the  surface  of  the  ground, 
but  the  material  proving  to  be  of  no  value  a  shaft  was  sunk  upon 
a  vein  which  penetrated  the  shales  at  this  point,  in  the  manner 
which  has  been  described  by  Eldridge.1  Some  of  the  material 
was  obtained  also  by  running  tunnels.  It  is  of  interest  in  this 
place  merely  to  determine  the  character  of  the  bitumen  which 
was  obtained. 

The  crude  material  was  found  in  different  degrees  of  purity 
and  containing  from  54  to  91  per  cent  of  bitumen,  as  appears 
from  the  following  analyses: 

FROM  DEPOSIT  OF  STANDARD  ASPHALT  COMPANY,  CALIFORNIA. 


Test  number  

13391 

13589 

13589 

13593 

13594 

Bitumen  bv  CS,,  air  temperature  . 
Difference                     

80.6% 
7.7 

No.  1 
90.5% 
0.0 

No.  2 

87.9% 
3.1 

54.3% 
6.2 

78.7% 
4.0 

Inorganic  or  mineral  matter  .... 

11  7 

9  5 

9  0 

39  5 

17  3 

Malthenes  : 
Bitumen  soluble  in  88°  naphtha, 
air  temperature 

100.0 
46  0 

100.0 
49  8% 

100.0 

43  1% 

100.0 
31  0% 

100.0 
41  o% 

This  is  per  cent  of  total  bitumen  . 
Loss  of  crude  at  212°  F  for  1  hour 

57.1 

55.0 

5.7% 

49.0 
14.9% 

57.1 

5.8% 

52.8 
5  9% 

Bitumen  yields  on  ignition: 
Fixed  carbon 

7  3 

The  crude  material  was  a  compact  homogeneous  brownish 
bitumen,  very  much  resembling  gilsonite  in  its  outward  appear- 
ance, but  being  very  much  softer.  Much  of  it,  although  showing 
no  outward  evidence  of  so  doing,  contained  an  appreciable  per 
cent  of  water  which,  together  with  a  certain  amount  of  gas,  is 
evolved  on  heating  to  100°  C.  In  some  cases  the  loss  reached 


*The  Asphalt  and  Bituminous  Rock  Deposits  of  the  United  States,  1901, 


449. 


INDIVIDUAL  ASPHALTS. 


205 


REFINED  STANDARD  ASPHALT,  CALIFORNIA. 

Test  number. 13601 

PHYSICAL  PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original  substance,  diy 1 .0627 

Color  of  powder  or  streak. Black 

Lustre Dull 

Structure Uniform 

Fracture Semi-conchoidal 

Hardness Soft 

Odor Asphalt  ic 

Softens 170°  F. 

Flows 180°  F, 

Penetration  at  78°  F. 0  to  27° 

CHEMICAL   CHARACTERISTICS. 

Dry  substance : 

Loss,  325°  F.,  7  hours 6.6% 

Character  of  residue Smooth 

Loss,  400°  F.,  7  hours  (fresh  sample) 19.9% 

Character  of  residue Blistered 

Bitumen  soluble  in  CS,  air  temperature 89 .8% 

Difference 3.4 

Inorganic  or  mineral  matter. 6.8 

100.0 

Malt  henes : 

Bitumen  soluble  in  88°  naphtha,  air  temperature 53 . 4% 

This  is  per  cent  of  total  bitumen 59 . 4 

Per  cent  of  soluble  bitumen  removed  by  H.jSO4 51 .9 

Per  cent  of  total  bitumen  as  saturated  hydrocarbons. ....  28.6 

Bitumen  soluble  in  62°  naphtha 60 .0% 

This  is  per  cent  of  total  bitumen 66 .8 

Carbenes : 

Bitumen  insoluble  in  carbon  tetrachloride,  ah*  temperature  0 . 3% 

Bitumen  yields  on  ignition: 

Fixed  carbon. 8.0% 

as  high  as  16  per  cent.    The  run  of  the  mine  would  average  above 

80  per  cent  of  bitumen  with  10  per  cent  of  mineral  matter  and 

5  per  cent  of  moisture  and  gas.    This  bitumen  is  more  particu* 


206  THE  MODERN  ASPHALT  PAVEMENT. 

larly  characterized  and  differentiated  from  ordinary  asphalts  by 
the  fact  that  it  yields  only  7  to  8  per  cent  of  fixed  carbon,  where 
the  asphalts  and  gilsonite  contain  14  to  15  per  cent. 

For  the  purpose  of  preparing  the  crude  material  for  use  in 
the  paving  industry  it  was  melted  with  the  addition  of  about  30 
per  cent  of  a  dense  asphaltic  flux.  The  resulting  product  was 
quite  hard  and  was  further  fluxed  for  the  purpose  of  making  an 
asphalt  cement.  This  material  was  in  use  to  a  considerable  extent 
in  the  middle  West  before  1900,  but  the  mine  became  exhausted 
and  it  is  no  longer  available. 

The  refined  material  had  the  characteristics  tabulated  on  p.  205. 

The  refined  Standard  asphalt  was  a  rather  pure  bitumen  carry- 
ing but  6.8  per  cent  of  mineral  matter  with  90  per  cent  of  bitu- 
men. The  percentage  of  malthenes  was  smaller  than  that  found 
in  Trinidad  and  Bermudez  asphalts,  but  the  softening  point  was 
lower  than  would  have  been  expected  in  such  a  case.  As  has 
been  said  the  fixed  carbon  which  this  material  yields  is  very  low. 
Except  for  this  its  general  outward  resemblance  to  gilsonite  would 
seem  to  point  to  the  fact  that  the  bitumen  from  the  Standard 
mine  must  be  closely  allied  to  it.  It  differs  from  it,  however, 
in  that  in  gilsonite  the  percentage  of  the  total  bitumens  present 
as  saturated  hydrocarbons  is  very  much  smaller.  This  may  be 
due,  however,  to  the  fact  that  in  gilsonite  metamorphism  has  gone 
much  further  than  in  the  case  of  the  bitumen  from  the  Standard 
mine.  Although  none  of  this  bitumen  is  available  for  paving 
purposes  at  the  present  day,  its  character  has  been  shown 
because  of  its  uniform  structure  and  resemblance  in  certain 
respects  to  gilsonite. 

Good  pavements  were  constructed,  with  the  Standard  bitumen 
where  it  was  properly  handled,  but  in  many  cases  the  surface 
failed  to  give  satisfaction  owing  to  lack  of  skill  in  its  use. 

Other  Deposits  of  Solid  Bitumen  in  California. — In  addition 
to  the  two  abandoned  deposits  of  asphalt  which  have  been  described, 
namely,  those  at  the  La  Patera  and  Standard  mines,  there  are 
numerous  others  scattered  throughout  Lower  California,  descrip- 
tions of  which  will  be  found  in  the  Eldridge  report  on  "The  Asphalt 
and  Bituminous  Rock  Deposits  of  the  United  States."  None  of 


INDIVIDUAL  ASPHALTS.  207 

them  have  proved,  although  development  has  been  attempted  in 
many  cases,  to  be  of  the  slightest  commercial  importance,  as  the 
material  available  at  any  one  point  is  too  small  to  pay  for  mining 
it,  owing  to  the  fact  that  the  bitumen  is  found  in  fissures  or  veins 
in  the  shales,  which  always  pinch  out  at  a  very  moderate  depth, 
due  to  the  pressure  exerted  by  the  superimposed  strata,  and  is 
often  mixed  with  such  a  large  proportion  of  the  mineral  matter 
from  the  vein  walls,  at  times  in  the  shape  of  brecciated  masses 
scattered  through  the  bitumen,  that  it  is  extremely  difficult  to 
handle.  The  only  interest  to  the  paving  industry  hi  these  deposits 
lies  in  the  fact  that  minute  percentages  of  them  have  at  times 
been  added  to  the  solid  residues  from  asphaltic  oils  hi  order  to 
substantiate  the  claim  that  the  latter  contained  native  solid  bitu- 
mens. As  a  paving  material  none  of  them  has  ever  amounted 
to  anything  nor  will  any  of  them  ever  do  so. 

SUMMARY. 

In  the  preceding  pages  the  characteristics  of  the  asphalts  which 
are  or  have  been  available  to  any  commercial  extent  are  given. 
The  supply  of  Trinidad  asphalt  is  extremely  large  in  amount, 
uniform  in  character,  and  much  more  stable  than  any  other,  owing 
to  the  character  of  the  hydrocarbons  of  which  it  is  composed. 
Bermudez  asphalt,  for  the  same  reason,  is  much  more  liable  to 
change.  Maracaibo  asphalt  differs  essentially  from  all  others  in 
several  respects.  The  data  in  regard  to  many  minor  deposits 
illustrate  the  very  considerable  variation  which  occurs  in  material 
included  under  the  specific  designation  asphalt. 


CHAPTER  XI. 


SOLID  NATIVE  BITUMENS  WHICH  ARE  NOT  ASPHALT. 

IT  appears  in  our  classification  of  native  bitumens  that  several 
solid  native  bitumens  exist  which,  from  their  peculiar  character- 
istics, cannot  be  included  among  the  asphalts.  These  include 
gilsonite,  grahamite,  manjak,  and  glance  pitch.  The  two  former 
are  t-he  only  ones  which  are  of  any  interest  in  the  paving  industry. 

Gilsonite. — The  occurrence  of  gilsonite  in  Utah  and  Colorado 
is  thoroughly  described  in  the  report  of  Eldridge,  which  has  been 
frequently  referred  to.  It  is  only  necessary  in  the  present  place 
to  consider  its  physical  properties  and  proximate  chemical  com- 
position. 

Gilsonite  is  one  of,  if  not  the  purest,  forms  of  solid  bitumen 
found  in  nature.  It  is  practically  entirely  soluble  in  carbon  di- 
sulphide.  It  varies  to  a  certain  extent  in  hardness  in  the  various 
deposits  and  veins  in  which  it  occurs.  The  extremes  in  composi- 
tion in  the  present  commercial  supply  appear  in  the  following 
table. 

GILSONITE. 

PHYSICAL  PROPERTIES. 


Test  number                                 

92603 

80343 

Specific  gravity,  78°  F./780  F.,  original  sub- 
stance dry  

1.044 

1  049 

Color  of  powder  or  streak  .  . 

Brown 

Brown 

Lustre                                            • 

Lustrous 

Lustrous 

Structure  

Homogeneous 

Homogeneous 

P  racture                  

Sub-conchoidal 

Sub-conchoidal 

ilnrdness  original  substance  . 

2 

2 

Softens  

260°  F. 

300°  F. 

Flows                         

275°  F. 

325°  F 

Penetration  at  78°  F  

0 

o 

206 


SOLID  NATIVE    BITUMENS,    NOT  ASPHALT. 

CHEMICAL  CHARACTERISTICS. 


209 


Dry  substance: 
Loss  325°  F  ,  7  hours  

.9% 

2.3% 

Smooth 

Intumesces 

Loss  400°  F  ,  7  hours  

1.2 

4.0 

Smooth 

Intumesces 

Bitumen  soluble  in  CSj,  air  temperature  .... 
Inorganic  or  mineral  matter  

99.0% 
.0 

99.9% 
.1 

1.0 

.0 

Malthenes: 
Bitumen  soluble  in  88°  naphtha,  air  temp. 
This  is  per  cent  of  total  bitumen  

100.0 

47.2 
47.7 

100.0 
15.9% 
15.9 

Per  cent  of  soluble  bitumen  removed  by 
H2SO4  

87.7 

71.8 

Per  cent  of  total  bitumen  as  saturated 
hydrocarbons    .                   

5.9 

4.5 

67.4% 

30.3% 

This  is  per  cent  of  total  bitumen  .        .    . 

68.1 

30.4 

Carbenes: 
Bitumen  insoluble  in  carbon  tetrachloride, 

.0% 

•4% 

Bitumen  yields  on  ignition: 
Fixed  carbon  .          

13.0% 

13.4% 

Gilsonite  is  known  in  the  trade  in  two  forms,  firsts  and  seconds, 
the  firsts  being  the  highest-grade  material  in  large  lumps  unac- 
companied by  powder,  while  the  seconds  are  that  part  of  the 
mineral  which  occurs  nearest  the  vein  walls,  and  in  fragmentary 
particles  and  are  made  up  of  the  less  attractive  product  of  the 
mine.  The  difference  in  these  two  grades  of  gilsonite  is  one  largely 
of  appearance  rather  than  quality  when  taken  from  the  same  vein. 

Gilsonite  is  the  purest  native  bitumen  with  which  we  are 
acquainted,  the  best  varieties  containing  99.5  per  cent  of  bitumen, 
and  with  but  traces  of  matter  not  of  a  bituminous  nature.  The 
bitumen  is  equally  soluble  in  cold  carbon  tetrachloride  and  carbon 
disulphide,  thus  differentiating  it  from  grahamite  and  some  of 
the  residual  pitches. 

Gilsonite  is  more  variable  when  taken  from  different  deposits 
and  at  different  depths. 


210  THE  MODERN  ASPHALT   PAVEMENT. 

The  density  of  this  bitumen  is  somewhat  smaller  than  that 
of  the  asphalts  and  it  has  a  much  higher  softening  point,  as  might 
be  expected  from  the  fact  that  it  is  brittle  and  readily  reduced 
to  a  reddish-brown  powder,  the  latter  characteristic  alone  differ- 
entiating it  from  the  other  native  bitumens  which  give  a 
much  blacker  powder.  As  would  be  expected  in  such  a  brittle 
material  the  percentage  of  malthenes  is  low,  only  48  per  cent 
of  the  total  bitumen  being  soluble  in  88°  naphtha.  The  amount 
will  vary,  however,  in  gilsonite  from  different  veins  and  from 
different  parts  of  the  vein,  weathered  material  at  times  contain- 
ing but  14  per  cent,  while  in  the  best  it  may  rise  to  over  70  per 
cent. 

The  hydrocarbons  composing  the  malthenes  of  gilsonite  are 
entirely  different  in  character  from  those  found  in  the  asphalts. 
They  are  almost  entirely  composed  of  unsaturated  hydrocarbons 
attacked  by  strong  sulphurs  acid,  and  this  fact  differentiates  gil- 
sonite completely  from  asphalt.  The  hydrocarbons  unattacked  by 
dilute  sulphuric  acid  are  extremely  viscous,  sticky,  and  resinous 
and  absolutely  different  from  those  found  in  any  other  native  bitu- 
men, and  there  seems  to  be  good  ground  for  the  inference  that  the 
other  hydrocarbons  composing  gilsonite  are  likewise  quite  different 
from  those  occurring  in  the  asphalts.  A  close  study  of  these 
hydrocarbons  will  be  of  great  interest,  but  our  information  at 
present  available  is  sufficient  to  justify  us  in  placing  gilsonite 
in  a  class  by  itself  among  the  native  bitumens.  Gilsonite  is  char- 
acterized by  yielding  the  same  percentage  of  fixed  carbon  on 
ignition  that  is  found  in  the  asphalts.  This  is  not  what  would  be 
expected  from  a  consideration  of  the  proximate  composition  of 
the  material,  which  would  lead  us  to  suppose  that  the  percentage 
would  be  higher.  In  material  which  is  much  weathered  a  higher 
percentage  is  actually  found,  reaching  in  one  instance  26  per 
cent,  and  corresponding,  of  course,  to  a  smaller  percentage  of 
naphtha  soluble  bitumen  in  the  material,  although  the  relation 
between  fixed  carbon  and  malthenes  is  by  no  means  a  constant 
one.  Gilsonite  is  readily  soluble  in  the  heavy  asphaltic  residues 
from  California  and  Texas  petroleums  and,  when  mixed  with 


SOLID  NATIVE  BITUMENS,  NOT  ASPHALT.  21 1 

this  in  the  proper  proportion,  makes  a  material  which  is  extremely 
rubbery  and  more  or  less  elastic  and  ductile. 

Gilsonite  in  the  Paving  Industry. — Gilsonite  has  been  used 
very  successfully  and  to  a  very  considerable  extent  in  the  paving 
industry,  the  peculiar  rubbery  nature  of  the  cement  produced 
from  it  with  a  heavy  asphaltic  flux,  and  the  fact  that  this  cement 
is  less  susceptible  to  temperature  changes  than  those  made  with 
the  ordinary  asphalts,  making  it  a  very  desirable  material.  It 
was  not  available  for  use,  at  least  in  the  East,  until  the  advent 
of  the  Texas  asphaltic  flux  in  1902,  as  the  paraffine  fluxes  will 
not  cut  Gilsonite  satisfactorily,  the  result  being  a  very  short 
and  granular  substance  which  has  no  cementing  power,  while 
the  California  fluxes  were  too  expensive.  Gilsonite  has  wide 
applications  in  many  industries.  Successful  pavements  have  been 
laid  with  it  which  have  been  in  use  for  years,  and  it  is  an  impor- 
tant constituent  of  varnishes,  insulations,  and  waterproofing  com- 
pounds. 

Grahamite. — Grahamite  is  a  brittle  black  bitumen,  rarely  of 
compact  structure,  which  does  not  melt  readily  but  merely  intu- 
mesces  on  heating  to  high  temperatures.  It  occurs  hi  veins  rather 
widely  disseminated,  but  never  in  large  amounts.  Its  physical 
properties  and  chemical  constitution  differentiate  it  from  all 
other  solid  bitumens.  Its  structure  is  distinguished  by  what 
has  been  called  a  hackly  or  pencillated  fracture  produced  appar- 
ently by  the  working  of  the  brittle  bitumen,  induced  by  the  move- 
ment of  the  vein  wall.  At  times  there  is  a  grosser  columnar 
structure.  As  types  of  this  material,  that  found  in  Oklahoma 
in  the  Ten  Mile  Creek  district,  in  the  Choctaw  Nation,  and  in 
Ritchie  County,  West  Virginia,  where  it  was  originally  discovered, 
will  serve.  These  characteristics  are  shown  by  the  analyses 
given  on  page  212. 

Grahamite  is  an  almost  entirely  pure  bitumen  soluble  in  carbon 
disulphide,  naphthalene,  and  dead  oil,  but  it  is  differentiated  from 
the  asphalts  and  gilsonite  by  the  fact  that  it  is  almost  entirely  insol- 
uble in  naphtha,  even  of  62°  density,  and  to  the  extent  of  55.0  per 


212 


THE  MODERN  ASPHALT  PAVEMENT. 
GRAHAMITE. 


Test  number    

68940 

75637 

Location  

West 

PHYSICAL   PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original  sub- 
stance dry              

1.171 

Virginia 
1.137 

Color  of  powder  or  streak  

Black 

Black 

Dull 

Dull 

Uniform 

Uniform 

Fracture   

Hackly 

friable 
Irregular 

Hardness  original  substance     

Brittle 

2 

Odor                             

None 

None 

Softens                             

Intumesces 

Intumesces 

t  ( 

<  < 

Penetration  at  78°  F  

0° 

0° 

CHEMICAL    CHARACTERISTICS. 

Dry  substance: 
Loss  325°  F    7  hours            

+  .1% 

Loss  400°  F    7  hours  (fresh  sample)  

+  .5% 

Bitumen  soluble  in  CS,  air  temperature    . 

94  1% 

97.8% 

Difference                                           

.2 

Inorganic  or  mineral  matter       

5  7 

2.1 

Malthenes: 
Bitumen  soluble  in  88°  naphtha,  air  temp 
This  is  per  cent  of  total  bitumen 

100.0 

.4% 
.4 

100.0 

3.3% 
3.37 

Per  cent  of  soluble  bitumen  removed  by 
H^SO 

25.0 

Per  cent   of    total  bitumen    as    saturated 
hydrocarbons                        

.32 

Bitumen  soluble  in  62°  naphtha  

.7% 

3.4% 

This  is  per  cent  of  total  bitumen  

Carbenes  : 
Bitumen  insoluble  in  carbon  tetrachloride, 
air  temperature                                           .  . 

68.7% 

3.47 
55.0% 

Bitumen    insoluble    in    hot    carbon    tetra- 
chloride                         

48.6 

1.3% 

Bitumen  yields  on  ignition: 

53.3% 

41.0% 

Ultimate  composition: 

86.56% 

8.68 

1.79 

2.97 

100.00 

SOLID   NATIVE   BITUMENS,    NOT    ASPHALT.  213 

cent  to  80.6  per  cent  in  cold  carbon  tetraehloride.  It  is  also  differ- 
entiated from  the  asphalts  and  gilsonites  by  the  fact  that  it  yields 
from  30  to  50  per  cent  of  fixed  carbon  on  ignition.  Grahamite, 
although  not  soluble  in  the  lighter  oils,  is  readily  dissolved  by 
the  denser  or  semi-asphaltic  fluxes,  and  in  this  condition  forms  a 
rubbery  material  quite  similar  to  that  produced  in  the  same  way 
with  gilsonite.  A  small  cylinder  of  it  when  bent  upon  itself  will 
rapidly  return  to  its  original  form.  It  lacks  ductility,  that  is  to 
say,  it  is  very  short  when  a  cylinder  of  it  is  drawn  out. 

A  similar  deposit  of  grahamite  is  found  in  Middle  Park,  Colo- 
rado. This  material  is  inaccessible  and  of  no  commercial  impor- 
tance. It  has  the  composition  given  on  page  214. 

It  is  apparent  from  the  results  of  the  analyses  of  the  3  gra- 
hamites  that  the  different  deposits  vary  in  the  degree  to  which 
the  molecule  has  been  condensed,  as  shown  by  the  percentage 
of  bitumen  insoluble  hi  cold  carbon  tetraehloride. 

It  has  also  been  found  that  grahamite  can  be  divided  into 
two  classes,  those  containing  sulphur  and  those  containing  oxygen. 

As  has  been  said,  numerous  deposits  of  grahamite  are  found 
in  Cuba,  Mexico,  Trinidad,  and  elsewhere,  but  they  are  of  no 
commercial  importance  as  far  as  the  asphalt  paving  industry  is 
concerned,  although  of  great  interest  from  a  purely  scientific 
point  of  view.  These  will  be  described  by  the  writer  in  another 
place. 

Grahamite  has  a  number  of  industrial  uses.  Successful  pave- 
ments have  been  constructed  with  it  in  combination  with  gilsonite 
and  heavy  asphaltic  fluxes.  Mastic  made  with  it  is  more  resistant 
to  grease  and  oil  than  the  ordinary  type,  and  it  has  been  made 
a  constituent  of  varnishes,  of  rubber  substitutes,  and  of  filler 
for  brick  and  stone  blocks.  When  cut  with  heavy  asphaltic  flux 
it  is  even  more  rubbery  and  elastic  than  gilsonite  under  the  same 
circumstances,  and  less  susceptible  to  heat. 

Glance  Pitch  and  Manjak. — These  bitumens  are  of  little  or 
no  interest  in  connection  with  the  paving  industry,  but  they  must 
be  mentioned  here  in  order  to  complete  our  description  of  the 
solid  native  bitumens. 

Glance  pitch  is  a  material  which  is  quite  widely  distributed 


214  THE  MODERN  ASPHALT  PAVEMENT. 

GRAHAMITE  FROM  MIDDLE  PARK,  COLORADO. 
Test  number 19162 

PHYSICAL   PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original  substance,  dry 1 .160 

Color  of  powder  or  streak Black 

Lustre Dull 

Structure Uniform- 
homogeneous 

Fracture Columnar, 

scaly 

Hardness,  original  substance 3 

Odor .* .  None 

Softens Intumesces 

Flows 

Penetration  at  78°  F 0° 

CHEMICAL   CHARACTERISTICS. 

Bitumen  soluble  in  CS2,  air  temperature 98 .2% 

Difference 1.7 

Inorganic  or  mineral  matter .1 

100.0 

Malthenes: 

Per  cent  total  bitumen  soluble  in  88°  naphtha,  air  tem- 
perature.    .8% 

Carbenes: 

Bitumen  insoluble  in  carbon  tetrachloride,  air  temperature          80 . 6% 

Bitumen  yields  on  ignition' 

Fixed  carbon 47.4% 

Ultimate  composition: 

Carbon 85.97% 

Hydrogen 7.65 

Sulphur .93 

Difference  (oxygen?) 5. 45 

100.00 

over  the  world,  although  the  best  supplies  come  from  the  East, 
Syria,  and  the  Dead  Sea. 

Manjak  is  found  only  in  the  island  of  Barbadoes.     A  bitumen 
is  shipped  from  Trinidad  under  the  name  of  manjak,  but  this 


SOLID  NATIVE  BITUMENS,  NOT  ASPHALT.  215 

material  is  really  a  grahamite  and  not  a  true  manjak,  as  it  does 
not  melt  and  has  all  the  properties  of  the  latter  bitumen. 

The  characteristics  of  these  materials  are  shown  by  the  follow- 
ing analyses: 

EGYPTIAN  GLANCE  PITCH. 

Test  number 14145 

PHYSICAL   PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original  substance,  dry 1 .097 

Color  of  powder  or  streak Black 

Lustre Lustrous 

Structure Brittle- 
uniform 

Fracture Conchoidal 

Hardness,  original  substance 2 

Softens 250°  F. 

Flows 260°  F. 

Penetration  at  78°  F 0° 

CHEMICAL    CHARACTERISTICS 

Bitumen  soluble  in  CS2,  air  temperature 99 . 7% 

Difference .2 

Inorganic  or  mineral  matter. .1 

100.0 

Malthenes: 

Bitumen  soluble  in  88°  naphtha,  air  temperature 23 . 5% 

This  is  per  cent  of  total  bitumen 23.6 

Per  cent  of  soluble  bitumen  removed  by  H^Of 72 . 0 

Bitumen  soluble  in  62°  naphtha 36.9% 

This  is  per  cent  of  total  bitumen 37.0 

Carbenes : 

Bitumen  insoluble  in  carbon  tetrachloride,  air  temperature  0.1% 

Bitumen  yields  on  ignition: 

Fixed  carbon 15.0% 

Ultimate  composition: 

Sulphur 8.52% 

Carbon 80.87 

Hydrogen 10.42 

Nitrogen .19 

100.00 


216  THE  MODERN  ASPHALT  PAVEMENT. 

BARBADOES  MANJAK. 
Test  number 14143 

PHYSICAL   PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original  substance,  dry 1 .0844 

Color  of  powder  or  streak Dark  brown 

Lustre Lustrous 

Structure Uniform 

Fracture Conchoidal 

Hardness,  original  substance 1 

Softens 230°  F. 

Flows 250°  F. 

Penetration  at  78°  F 0° 

CHEMICAL   CHARACTERISTICS. 

Bitumen  soluble  in  CS2,  air  temperature 99 . 2% 

Difference .5 

Inorganic  or  mineral  matter .3 

100.0 

Malthenes: 

Bitumen  soluble  in  88°  naphtha,  air  temperature 26 .9% 

This  is  per  cent  of  total  bitumen 27.0 

Per  cent  of  soluble  bitumen  removed  by  HjSO4 75 .0 

Bitumen  soluble  in  62°  naphtha 40 . 4% 

This  is  per  cent  of  total  bitumen 40 . 7 

Carbenes : 

Bitumen  insoluble  in  carbon  tetrachloride,  air  temperature  1.2% 

Bitumen  yields  on  ignition : 

Fixed  carbon 25.0 

It  will  be  noted  that  glance  pitch  is  a  very  brittle  material, 
of  a  higher  density  and  much  higher  melting-point  than  asphalt, 
of  great  purity  and  containing  but  a  very  small  percentage  of 
malthenes.  It  has  evidently  originated  in  the  very  complete 
hardening  of  asphalt  either  by  natural  causes  or,  exceptionally, 
by  its  exposure  to  heat  in  one  way  or  another. 

Manjak  resembles  it  in  many  respects,  but  is  distinguished 
from  it  by  being  more  closely  related  to  grahamite,  on  account 
of  the  higher  percentage  of  fixed  carbon  which  it  contains,  that 
obtained  from  glance  pitch  being  an  amount  normal  to  asphalt, 


SOLID  NATIVE  BITUMENS,  NOT  ASPHALT.  217 

while  that  from  manjak  approaches  that  obtained  from  grahamite. 
It  is,  however,  differentiated  from  grahamite  by  the  fact  that  it 
actually  melts,  instead  of  intumescing  only,  and  dissolves  com- 
pletely in  cold  carbon  tetrachloride. 

In  both  of  these  solid  bitumens  there  is  a  very  small  propor- 
tion of  stable  hydrocarbons  unattacked  by  sulphuric  acid. 

Ozocerite. — Ozocerite  is  a  solid  bitumen  the  principal  supply 
of  which  is  found  hi  Galicia.  A  small  amount  of  it  is  also  found 
in  Utah,  in  Emery  and  Uintah  Counties.  The  hydrocarbons  of 
which  it  is  composed  are  solids,  resembling  paraffine  scale.  When 
purified  it  is  known  as  ceresin  and  is  used  for  the  adulteration  of 
beeswax,  and  as  a  substitute  for  paraffine  scale,  which  it  is  superior 
to  on  account  of  its  high  melting-point.  As  it  is  a  paraffine  com- 
pound it  is  of  no  interest  in  the  paving  industry. 

PYROBITUMENS. 

Albertite. — Albertite  is  an  extremely  brittle  and  lustrous 
material.  It  was  first  described  by  Wetherill.1  It  "  occurs  fill- 
ing an  irregular  fissure  in  rocks  of  the  Subcarboniferous  Age  in 
Nova  Scotia."  It  has  since  been  found  in  Cuba,  Mexico,  Okla- 
homa, and  Utah.  It  is  not  a  true  bitumen,  but  a  very  small 
part  of  it  being  soluble  in  the  usual  solvents  for  that  substance. 
It  yields  a  very  high  percentage  of  fixed  carbon.  Analyses  of 
albertites  from  various  localities  which  have  been  examined  in 
the  author's  laboratory  are  tabulated  on  pages  218,  219. 

Its  ultimate  composition  is,  for  the  Nova  Scotia  material, 

Carbon 85 . 53% 

Hydrogen 13.20 

Sulphur 1 .20 

Nitrogen 42 

Albertite  is  usually  quite  free  from  mineral  matter,  but  in  the 
case  of  that  found  in  Mexico  it  contains  22.6  per  cent  and  a  rather 
larger  portion  of  bitumen  soluble  in  carbon  disulphide  than  in 
that  found  elsewhere. 

The  material  is  of  no  importance  in  the  paving  industry. 

1  Trans.  Am.  Phil.  Soc.,  Phila.,  1852,  353. 


218 


THE  MODERN  ASPHALT  PAVEMENT. 

ANALYSES  OF 


Nova 
61486 

Scotia 
7834 

1.075 
Black 

Lustrous 

Homogeneous 
Smooth 

Test  number  

PHYSICAL   PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original  sub- 
stance, dry  

Color   

Black 

Lustrous 

Homogeneous 
Smooth 

Lustre  

Structure  

Odor  

None 
Intumesces 

ii 

0° 

None 
Intumesces 

ii 

0° 

Softens  

Flows  

Penetration  at  78°  F             .           ... 

CHEMICAL   CHARACTERISTICS. 

Original  substance  : 
Loss,  212°  F.,  until  dry  

Dry  substance  : 
Bitumen  soluble  in  CS2,  air  temperature.  .  .  . 
Difference  

9.0% 
91.0 
.2 

100.2 

5.9% 
94.1 
.0 

100.0 
1.5% 

Inorganic  or  mineral  matter     

Malthenes: 
Bitumen  soluble  in  88°  naphtha,  air  tem- 
perature   

This  is  per  cent  of  total  bitumen  

Bitumen  yields  on  ignition  : 

39.0% 

29.8% 
1-2% 

Sulphur        

Wurtzilite. — Wurtzilite  is  a  hard  lustrous  pyrobitumen, 
slightly  elastic  in  thin  fragments,  which  is  found  in  Uintah  County, 
Utah.  It  does  not  fuse  at  high  temperatures,  but  a  process  has 
been  devised  for  fluxing  it  with  heavy  malthas  by  gradually  crack- 
ing it  at  high  temperatures.  It  is  practically  insoluble  in  car- 
bon disulphide  and  heavy  residuum. 


SOLID  NATIVE  BITUMENS,   NOT  ASPHALT. 
ALBERTITE. 


219 


Utah. 

Utah. 

Mexico. 

Cuba. 

Oklahoma. 

19187 

30495 

36326 

62989 

74995 

74995 

Bright 

Dull 

sample 

sample 

1.092 

1.099 

1.204 

Black 

Brown- 

Black 

Black 

black 

Partly 
lustrous 

Partly 
lustrous 

Dull 

Lustrous 



Homogeneous 

Irregular 

Irregular 

Irregular 

Semi- 
conchoidal 

Brittle 

2 

2 

2 

None 

None 

None 

None 

Does  not 

Intumesces 

Intumesces 

Intumesces 

intumesce 

it 

i  « 

it 

-Oo 

0° 

0° 

0° 

2.25% 

.2% 

.1% 

5.6% 

3.4% 

11.9% 

•  *  /%j 

Trace 

1.6% 

6.8% 

94.2 

96.4 

61.9 

98.9% 

87.7 

71.2 

.2 

.2 

26.2 

1.1 

10.7 

22.0 

100.0 

100.0 

100.0 

100.0 

100.0 

100.0 

Trace 

3  2% 

.0% 

.0% 

**  •    /o 
23.4 

•  v*  /%} 

37.0% 

40.4% 

39.0% 

53.0% 

33.6% 

54.2% 

1.06 

The  amount  available  is  too  small  to  make  it  of  any  impor- 
tance in  the  paving  industry,  and  this  and  the  preceding  pyro- 
bitumen  have  been  merely  mentioned  to  complete  our  illustra- 
tion of  the  various  types  which  are  found  in  nature.  Some  deter- 
minations of  its  characteristics  resulted  as  follows: 


220 


THE  MODERN  ASPHALT  PAVEMENT. 
WURTZILITE. 


Test  number.  

15270 

31724 

72684 

PHYSICAL   PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original 

substance,  dry 

1  0544 

1  0490 

1  0639 

CHEMICAL   CHARACTERISTICS. 

Bitumen  soluble  in  CS2,  air  temperature 

12  8% 

6  7% 

Bitumen  yields  on  ignition  : 
Fixed  carbon  

8  8% 

5  2% 

8.3% 

SUMMARY. 

The  several  solid  native  bitumens  which  are  not  asphalts  are 
shown  to  have  interesting  characteristics  and  some  valuable 
properties. 

Grahamite,  like  gilsonite,  can  be  fluxed  with  asphaltic  oils  at 
very  high  temperature  and  in  such  form  makes  a  very  rubbery 
material  of  value  in  the  paving  industry  as  well  as  for  paint  and 
varnish  and  for  waterproofing.  The  use  of  Grahamite  in  the 
construction  of  pavements  is  limited  by  the  fact  that  it  may  be 
utilized  only  at  high  temperatures  with  certain  modifications  and 
that  the  supply  is  extremely  small. 

The  other  solid  bitumens  are  of  interest  only  in  connection 
with  the  manufacture  of  varnishes  and  for  insulating  purposes; 
they  do  not  offer  inducements  towards  introducing  them  into 
the  paving  industry. 


CHAPTER  XII. 
ASPHALTIC  SANDS  AND  LIMESTONES. 

Kentucky. — Sands  are  found  in  Carter  and  Boyd  Counties  in 
the  northeastern  part  of  Kentucky  and  in  the  counties  of  Brecken- 
ridge,  Grayson,  Edmonson,  Warren,  and  Logan  in  the  western 
part  of  the  State.  The  geological  relations  of  these  sands  and 
the  manner  of  their  occurrence  is  described  in  great  detail  by 
Eldridge.1 

In  the  present  place  it  will  only  be  necessary  to  show  the  nature 
of  the  sands  and  that  of  the  bitumen  with  which  they  are  impreg- 
nated in  order  to  determine  their  availability  for  paving  purposes. 

In  a  general  way  it  may  be  said  that  the  sands  are  all  com- 
posed of  loose  grains  which  fall  to  pieces  on  the  extraction  of  the 
bitumen  and  are  in  no  case  sandstone.  The  bitumen  impregna- 
ting the  sand  is  not  a  solid  one,  but  consists  of  a  maltha  which 
pulls  out  to  a  long  thread  at  ordinary  temperature  or,  in  rare 
instances,  after  extraction  has  a  penetration  as  low  as  60°.  The 
bitumen  from  the  Green  River  sand  which  was  extracted  with 
carbon  disulphide  had  the  following  characteristics: 

BITUMEN  EXTRACTED   FROM  BITUMINOUS  SAND  FROM  THE 
GREEN  RIVER  DEPOSIT,  KENTUCKY. 

Penetraton  at  78°  F 60° 

Per  cent  of  total  bitumen  soluble  in  88°  naphtha ....  65 . 4 
Per  cent  of  soluble  bitumen  acted  upon  by  HjSO4 . .   15.0 

Bitumen  contains  soft  paraffines 2 . 6% 

Yields  on  ignition : 

Fixed  carbon 15  .C% 

It  appears  from  the  preceding  figures  that  the  bitumen  of  the 
Kentucky  sands  is  semi-asphaltic  in  that  it  yields  an  amount  ef 

1  The  Asphalt  and  Bituminous  Rock  Deposits  of  the  United  States,  1901. 

221 


222 


THE  MODERN  ASPHALT  PAVEMENT. 


fixed  carbon  corresponding  to  that  found  in  the  asphalts,  but  at 
the  same  time  contains  some  soft  paraffine  scale,  and  is  largely 
made  up  of  stable  hydrocarbons  which  are  not  attacked  by  sul- 
phuric acid.  As  a  rule,  the  bitumen  is,  however,  too  soft  to  be 
suitable  for  use  as  a  paving  cement  until  the  volatile  oils  have 
been  driven  off  by  heating.  When  the  bitumen  is  heated,  how- 
ever, it  is,  as  in  the  case  of  the  California  Carpinteria  sands,  rapidly 
converted  into  a  hard  pitch.  The  Kentucky  sands  contain  on  the 
average  about  6.5  per  cent  of  bitumen  of  the  nature  which  has  been 
described.  In  exceptional  cases  it  reaches  13  per  cent.  The 
characteristics  of  the  sands  in  particular  localities  are  as  follows: 

Carter  County. — A  deposit  of  bituminous  sand  occurs  on  Soldier 
Creek  in  Carter  County,  as  described  by  Eldridge.  Samples  of 
this  sand  analyzed  in  the  author's  laboratory  in  1898  and  1900 
had  the  following  composition: 

BITUMINOUS  SAND  FROM  SOLDIER  CREEK,  CARTER  COUNTY, 

KENTUCKY. 


Test  number  

10681 

33896 

Bitumen  soluble  in 

cs,  . 

1898 

8  2% 

1900 
9  1% 

Passing  200-mesh  s 

ieve  

4.5 

3  9 

"        100- 

1  1 

21.2 

35.0 

"         80- 

tt 

31  0 

36  0 

"         50- 

tt 

27  6 

15  0 

"         40- 

it 

3  5 

1  0 

"         30- 

if 

2  8 

0  0 

20- 

tt 

1.2 

0.0 

100.0 

100.0 

The  extracted  bitumen  is  a  soft  maltha  flowing  slowly  at  78°  F., 
and  hardening  rapidly  on  heating,  with  a  loss  of  12  per  cent. 

Breckenridge  County. — The  sandstones  of  Breckenridge  County 
are  worked  by  the  Breckenridge  Asphalt  Company  and  lie,  accord- 
ing to  Eldridge,  two  miles  south  of  Garfield,  in  a  bed  14  feet  thick, 
the  lower  7  or  8  feet  being  much  more  enriched  than  the  upper 
portion.  Specimens  examined  in  the  author's  laboratory  had 
the  following  composition: 


ASPHALT1C  SANDS  AND  LIMESTONES. 


223 


BITUMINOUS    SAND    FROM    DEPOSIT    OF    BRECKENRIDGE    AS- 
PHALT  COMPANY,  BRECKENRIDGE  COUNTY,  KENTUCKY. 

TEST  No.  9264. 


Richer  Portion. 

Poorer  Portion. 

Bitumen  soluble  in  CS2  
Passing  200-mesh  sieve       .  . 

7.7% 
7.2 

4.3% 
10.6 

"       100-    "        '  '    

26.6 

26.6 

«         80-    "        "   

26.0 

26.0 

"         50-    "        "   

tt                 4Q_       H               tt 

29.4 
2.5 

29.4 
2.5 

ft                    QA           It                 tt 

0.4 

0.4 

tt         20-    "        " 

0.2 

0.2 

100.0 

100.0 

The  extracted  bitumen  is  a  soft  maltha  hardening  on  heating, 
as  is  the  case  with  bitumens  from  other  Kentucky  sands. 

Grayson  County. — Asphaltic  sands  are  found  in  Grayson  County 
in  the  neighborhood  of  Leitchfield,  which  Eldridge  describes  under 
the  designation  "  Schillinger  Prospects  "  and  "  Breyfogle  Quarries." 
At  the  latter  point  sands  impregnated  with  bitumen  and  seepages 
of  a  gummy  consistency  are  found.  The  sands  are  of  varying 
degrees  of  richness  and  the  seepages  of  different  degrees  of  hard- 
ness. The  results  of  analyses  of  specimens  of  the  materials  which 
were  formerly  mined  at  this  point  are  given  in  the  following  tables 
and  in  one  on  p.  225: 

ASPHALTIC  SANDS,  GRAYSON  COUNTY,  KENTUCKY. 


Test  number               

41187 

41277 

41188 

49577 

Bitumen  soluble  in  CS2  

6% 

10% 

13% 

13.7% 

Passing  200-mesh  sieve  

4 

13 

5 

4.3 

'  <       100-             '  '    

6 

63 

6 

4.0 

"         80-             "         .... 

3 

11 

6 

6.0 

"         50-             "        

5 

3 

52 

34.0 

"         40-              "    

7 

0 

18 

24.0 

"         30-             "   

20 

0 

0 

8.0 

"         20-              "    

29 

0 

0 

3.0 

"         10-             "           .... 

13 

0 

0 

3.0 

Retained  on  10-mesh  sieve    .... 

7 

0 

0 

100 

100 

100 

100.0 

224 


THE  MODERN  ASPHALT  PAVEMENT. 


BITUMEN  IMPREGNATING  MINERAL  MATTER,  GRAYSON 
COUNTY,  KENTUCKY. 


Test  number          

41189 

41190 

Specific  gravity,  78°  F./789  F  

1.282 

1.769 

Color          

Black 

Black 

Lustre  

Shining 

Shining 

Structure                      

Massive 

Massive 

Fracture                  

Irregular 

Irregular 

Hardness        

Odor     

Asphaltic 

Asphaltic 

Loss  220°  F    1  hour        .          

7.0% 

1.5% 

Bitumen  soluble  in  CS2,  air  temperature  
Difference 

6291% 

30.0% 
4  9 

iziorganic  or  mineral  matter 

28  4 

65  1 

Malthenes: 
Bitumen  soluble  88°  naphtha,  air  tempera- 
ture        

100.0 
50.8% 

100.0 
21.9% 

This  is  per  cent  of  total  bitumen 

83  0 

70  3 

Bitumen  soluble  62°  naphtha,  air  tempera- 
ture                                   

54  3% 

29  7% 

This  is  per  cent  of  total  bitumen  

87.0 

79  0 

fiitumen  yields  on  ignition: 
Fixed  carbon 

12  0% 

12  0% 

Penetration  of  extracted  bitumen  at  78°  F.  . 

45° 

35° 

It  will  be  noticed  that  in  the  case  of  the  sand  some  of  it  is 
quite  rich  in  bitumen  and  other  parts  of  it  quite  poor.  The  sand 
grains  are  extremely  coarse,  the  majority  of  them  being  of  50- 
and  40-mesh  size  in  one  instance,  and  larger  than  30  in  another. 
Such  a  sand  grading  alone  would  make  this  material  unsuitable 
for  use  in  an  asphalt  surface. 

The  mixture  of  loose  mineral  matter  and  asphalt  contains  a 
large  percentage  of  bitumen  which  is  very  hard  in  consistency 
but  is  hardly  asphaltic  in  nature,  as  the  amount  of  fixed  carbon 
which  it  yields  is  only  12  per  cent. 

The  seepages  vary  in  consistency  from  that  of  a  mere  maltha 
to  that  of  a  bitumen  having  a  penetration  of  only  35°.  In  the 


ASPHALTIC  SANDS  AND  LIMESTONES. 


225 


SEEPAGES,  GRAYSON  COUNTY,  KENTUCKY. 


41192 

41277 

Rnprifip  trravitv  78°  F  /78°  F 

9783 

Loss  220°  F  ,  1  hour  

26.8% 

19.2% 

Dry  substance  : 
Loss  325°  F  ,  7  hours  

4.1% 

'  '   ,  400°  F.  ,  "    "     (fresh  sample)  

12.4 

Character  of  residue  after  325°  F     

Too   soft   for 

"         "       "         "     400°  F  

penetration. 
22° 

Bitumen  soluble  in  CS2,  air  temperature  

89.8% 
0.3 

88.6% 
5.5 

Inorganic  or  mineral  matter   

9.9 

5.9 

Malthenes: 
Bitumen  soluble  in  88°  naphtha,  air  tem- 
perature                                    

100.0 

74  5% 

100.0 
54.0% 

This  is  per  cent  of  total  bitumen   

83  0 

61.2 

Bitumen  soluble  in  62°  naphtha,  air  tem- 
perature 

81  0% 

CO  8% 

This  is  per  cent  of  total  bitumen 

90  2 

68  7 

Bitumen  yields  on  ignition  : 
Fixed  carbon                           .               .    . 

15.6% 

Penetration  of  extracted  bitumen  at  78°  F.  .  . 



35° 

latter  case  the  material  seems  to  be  more  asphaltic,  as  it  yields 
15.6  per  cent  of  fixed  carbon. 

A  deposit  identified  to  the  author  as  being  from  Ferry's  quarry, 
in  Grayson  County,  has  the  following  characteristics: 

BITUMINOUS    SAND    FROM    FERRY'S    QUARRY,    GRAYSON 

COUNTY,  KENTUCKY. 

TEST  No.  7218. 

Bitumen  soluble  in  CS2 7.7% 

Passing  200-mesh  sieve 17.7 

"       100-    "        "    34.5 

"         80-    "        "    36.4 

"         50-    "        "   .  3.7 


100.0 

EXTRACTED   BITUMEN. 

Bitumen  soluble  in  88°  naphtha,  air  temperature  71 .4% 

Loss,  400°  F.,  7 hours 18.6 

Penetration  at  78°  F. .  .  81° 


226 


THE  MODERN  ASPHALT  PAVEMENT. 


This  material  is  composed  of  an  extremely  fine  sand,  quite 
different  from  that  found  at  the  Breyfogle  quarry,  and  contains 
between  7  and  8  per  cent  of  bitumen,  which,  after  heating  for  7 
hours  at  400°  F.;  loses  18.6  per  cent.  This  bitumen,  before  heat- 
ing, has  a  penetration  of  81°. 

Edmonson  County. — Eldridge  states  that  in  Edmonson  County 
there  are  many  deposits  of  asphaltic  sandstone  and  small  tar 
springs,  none  of  which  he  considers  to  be  of  any  value.  They  have 
not  been  examined  in  the  author's  laboratory. 

Warren  County. — Along  the  Green  River,  in  Warren  County, 
are  deposits  of  bituminous  sand  which  have  been  worked  for 
paving  purposes,  the  characteristics  of  which  are  that  they  con- 
sist of  quartz  sand  impregnated  with  from  6  to  9  per  cent  of  very 
soft  maltha. 

At  Youngs  Ferry  the  Green  River  Asphalt  Company  has  opened 
a  quarry  the  sand  from  which  has  the  following  compositions: 

BITUMINOUS  SAND  FROM  DEPOSIT  OF  GREEN  RIVER  ASPHALT 
COMPANY,  WARREN  COUNTY,  KENTUCKY. 


Test  number 

61873 

6.1% 
14.9 
48.0 
19.0 
12.0 
0.0 
0.0 
0.0 
0.0 

27606 

8.8% 
11.3 
10.0 
23.0 
37.1 
8.0 
.9 
.9 
.0 

Bitumen  solub 
Passing  200-me 
100- 
80- 
'"          50- 
40- 
30- 
20-    ' 
10-    ' 

Loss,  212°  F., 

einC 

;sh  sie 

t        ( 
i        < 

L  houi 

s, 

ve 

i 
t 

100.0 

100.0 
1.5% 

EXTRACTED    BITUMEN. 

Penetration  at  78°  F Too  soft,  pulls  to  a  thread 

Fixed  carbon 11.8% 

The  first  column  represents  the  average  composition  of  that 
which  has  been  taken  out  for  paving  purposes.  It  is  very  evi- 
dent that  the  small  percentage  of  bitumen  in  this  sand,  aside 


ASPHALTIC  SANDS  AND  LIMESTONES.  227 

from  the  fact  that  it  is  not  of  a  strictly  asphaltic  nature,  as  it 
yields  but  11.8  per  cent  of  fixed  carbon,  would  make  it  impossible 
to  produce  a  satisfactory  surface  mixture  with  it  without  some 
amendment. 

Near  Brownsville  the  Rock  Creek  Natural  Asphalt  Company 
has  worked  another  sand  which  is  coarser  than  that  found  at 
Youngs  Ferry,  as  shown  by  the  following  analysis: 

BITUMINOUS  SANDSTONE  NEAR  BROWNSVILLE,  KENTUCKY. 
TEST  No.  61363. 

Bitumen  soluble  in  CS2 6.6% 

Passing  200-mesh  sieve 12.4 


100- 
80- 
50- 
40- 
30- 
20- 
10- 


7.0 

3.0 

18.0 

30.0 

13.0 

6.0 

4.0 

100.0 


This  material,  like  that  from  the  Youngs  Ferry  deposit,  is 
not  sufficiently  rich  hi  bitumen  to  make  it  of  any  value. 

Oozings  of  this  bitumen,  collected  in  drill-holes,  had  the  com- 
position given  in  table  on  page  228  under  test  No.  40894. 

The  bitumen  in  the  sands  at  this  point  is  a  very  soft  one, 
having  a  penetration  of  193°.  It  hardens  rapidly  on  heating, 
the  residue  after  7  hours  at  400°  F.  having  a  penetration  of  only 
12°.  Such  an  unstable  bitumen,  aside  from  the  unsatisfactory 
grading  of  the  sand,  makes  this  sand  unavailable  for  the  produc- 
tion of  a  satisfactory  pavement. 

Logan  County. — Eldridge  states:  "The  deposits  of  bituminous 
sandstone  in  Logan  County  lie  in  its  northern  half.  ...  A  single 
quarry  of  the  Standard  Asphalt  Company  has  been  opened  about 
5  miles  northeast  of  Russellville." 

The  average  material  from  the  base  of  the  quarry  has  the  com- 
position given  in  table  on  page  228,  test  No.  19938. 

The  bitumen  which  oozes  from  the  sand  has  been  examined 
with  the  results  given  in  table  on  page  229. 


228  THE  MODERN  ASPHALT  PAVEMENT. 

OOZINGS  OF  BITUMEN  FROM  NEAR  BROWNSVILLE,  KENTUCKY. 

TEST  No.  40894. 
Loss,  212°  F.,  until  dry 22.8% 

DRY   SUBSTANCE. 

Loss,  325°  F.,  7  hours 11.5% 

Residue  after  heating  to  325°  F Penetration  =  55° 

Loss,  400°  F.  for  7  hours  (fresh  sample) 13 . 1% 

Residue  after  heating  to  400°  F Penetration  =  12° 

Bitumen  soluble  in  CS2,  air  temperature 94 . 4% 

Difference .5 

Inorganic  or  mineral  matter 5.1 

100. 0 

Malthenes : 

Bitumen  soluble  in  88°  naphtha,  air  tem- 
perature   75.6% 

This  is  per  cent  of  total  bitumen.  .... 80 .0 

Bitumen  soluble  in  62°  naphtha,  air  tem- 
perature   82.6% 

This  is  per  cent  of  total  bitumen 88 . 0 

EXTRACTED    BITUMEN. 

Penetration  a  78°  F  = 193° 

BITUMINOUS  SANDSTONE,  LOGAN  COUNTY,  KENTUCKY. 
TEST  No.  19938. 

Bitumen  soluble  in  CS2 7.8% 

Passing  200-mesh  sieve 6.2 

"        100-    "        "   27.0 

"         80-    "        " 31.0 

"         50-    "        "   ..  25.0 

40-    "        "   2.0 

"         30-    "        "   1.0 

100.0 
Loss  at  212°  F *.5% 

These  results  show  that  this  material,  like  the  bitumen  in 
the  sands  from  other  parts  of  Kentucky,  is  a  maltha  which 
hardens  on  heating  to  a  very  brittle  substance,  and  on  that  account 
is  not  suitable  for  paving  purposes. 


ASPHALTIC  SANDS  AND  LIMESTONES.  229 

BITUMEN  OOZING  FROM  SAND,  LOGAN  COUNTY,  KENTUCKY. 
TEST  No.  21264. 

Loss,  212°  F.,  until  dry 16.3% 

Dry  substance: 

Loss,  325°  F.,  7  hours 5.5% 

Residue  after  heating  to  325°  F Too  soft  for 

penetration 

Loss,  400°  F. ,  7  hours 3.8% 

Residue  after  heating  to  400°  F Penetra- 
tion =20° 
Bitumen  soluble  in  CS2,  air  temperature. .  .     62.8% 

Difference 7.7 

Inorganic  or  mineral  matter 29 . 5 

100.0 

Malthenes : 

Bitumen  soluble  in  88°  naphtha,  air  tem- 
perature   35 . 4% 

This  is  per  cent  of  total  bitumen 56 . 4 

Bitumen  soluble  in  62° naphtha, air  tem- 
perature   50 . 6% 

This  is  per  cent  of  total  bitumen 80 . 6 

Importance  of  the  Kentucky  Bituminous  Sands  for  the  Paving 
Industry. — From  the  preceding  data  it  is  very  evident  that  no 
satisfactory  asphalt  pavements  can  be  constructed  from  any  of 
the  bituminous  sands  available  in  Kentucky  for  two  reasons. 
In  the  first  place  the  bitumen  is  a  maltha  which  has  no  stability 
and  hardens  very  much  on  exposure  to  high  temperatures.  In 
the  second  place  it  is  not  present  in  sufficient  amount  to  cement 
the  sand  grains  together  satisfactorily,  and  finally,  the  sand  itself 
is  seldom  graded  in  a  way  to  form  a  satisfactory  mineral  aggregate. 
It  is  always  deficient  in  filler.  It  may  be  possible,  for  light  traffic 
streets,  to  make  an  asphalt  surface  mixture  from  a  Kentucky 
sand  by  the  addition  of  some  hard  bitumen  and  a  satisfactory 
amount  of  filler,  but  when  this  is  done  it  would  generally  be  found 
to  have  been  a  matter  of  economy  not  to  have  used  the  bituminous 
sand  at  all,  but  to  have  started  with  a  suitable  local  sand  and  have 
combined  this  with  a  proper  asphalt  cement  and  a  good  filler. 

Actual  experience  with  asphalt  pavements  constructed  with 


230  THE  MODERN  ASPHALT  PAVEMENT. 

Kentucky  material  has  confirmed  all  these  conclusions,  and  it  is 
safe  to  say  that  the  sooner  the  attempt  to  work  these  deposits  is 
abandoned  the  less  money  will  be  sunk. 

Oklahoma. — Deposits  of  bitumen  in  various  forms  are  found 
widely  scattered  over  this  State.  Among  them  are  several 
which  consist  of  bituminous  sands.  Although  none  of  them 
is  of  any  great  value  in  the  paving  industry,  it  will  be  of  interest 
here  to  show  what  their  composition  is  in  order  that  vain 
attempts  may  not  be  made  to  utilize  them  at  great  financial 
loss. 

Limestones  saturated  with  bitumen  are  also  found  in  the 
immediate  neighborhood  of  the  bituminous  sands,  and  as  attempts 
have  been  made  to  utilize  these  in  conjunction  with  the  sands 
they  will  be  described  at  the  same  time. 

In  what  Eldridge  denominates  the  Buckhorn  District,  in  the 
region  east  of  the  Washita  River  and  in  the  neighborhood  of  Rock 
Creek,  numerous  quarries  of  bituminous  sands  and  limestones  have 
been  opened  by  different  individuals  and  companies  and  some  of  the 
material  has  been  utilized  in  the  construction  of  street  pavements. 

The  material  from  the  Ralston  quarry,  about  2  miles  west- 
northwest  of  Schley  and  8  miles  northeast  of  Dougherty,  has  the 
following  composition.  This  material  is  still  further  described 
by  Eldridge.1 

FROM  RALSTON  QUARRY,  NEAR  SCHLEY  AND  DOUGHERTY, 

OKLAHOMA. 

TEST  No.  11602. 

Bitumen  soluble  in  CS2 5.0% 

Passing  200-mesh  sieve 9.7 

"       100-    "        lt   41.0 

"         80-    "        "   29.0 

50-    "        "   11.0 

40-    "        "   2.0 

30-    "        "   1.0 

"         20-    "        "   1.0 

"         10-    "        " 3 

100.0 
1  The  Asphalt  and  Bitumimous  Deposits  of  the  U.  S.,  1901,  294. 


ASPHALTIC  SANDS  AND  LIMESTONES. 


231 


EXTRACTED   BITUMEN. 

Extracted  bitumen :  a  soft  maltha,  consistency  of  residuum. 

Loss,  325°  F. ,  7  hours 5.96% 

"      400°  F.,  5     "      (fresh  sample) .        9.98% 

Residue  after  heating  to  400°  F Pulls  to  a  long 

thin  thread 
and     pene- 
trates 76°. 

The  Gilsonite  Roofing  and  Paving  Company's  mines  of  bitu- 
minous limestone  and  asphaltic  sands  are  found  in  Sections  21, 
22,  and  23,  Range  R.3.E.  The  Rock  Creek  Natural  Asphalt 
Company  own  and  have  somewhat  developed  several  deposits 
of  bituminous  sands  and  limestone  rocks  north  of  the  preceding 
deposits,  in  the  Buckhorn  District. 

The  sands  which  have  been  developed  to  the  greatest  extent 
and  used  by  the  Rock  Creek  Natural  Asphalt  Company  have  the 
following  composition: 

BITUMINOUS  SAND  FROM  BUCKHORN  DISTRICT,  OKLAHOMA. 


Test  number  

30481 

12.2% 
1.8 
29.0 
26.0 
30.0 
1.0 

100.0 

69086 

11-1% 
12.9 
48.0 
23.0 
5.0 
0.0 

100.0 
Soft 

Bitumen  soluble  in 
Passing  2CO-mesh  s 
"        100-    " 
80-    " 
50-    " 
40-    " 

Extracted  bitumen 

CS, 

icve 

<  < 

n 

i  ( 

(  t 

at  78°  F 

This  sand  is  fine  and  somewhat  variable  in  grading,  the  bitu- 
men which  it  contains  is  a  soft  maltha,  although  it  varies  some- 
what in  accordance  with  the  extent  to  which  it  has  been  weathered. 
The  material  has  been  combined  with  the  limes  tqnes,  a  description 
of  which  follows,  and  fairly  successful  pavements  have  resulted 
from  the  combination  in  Kansas  City,  Mo. 

The  principal  bituminous  limestone  quarries  of  the  Gilsonite 
Roofing  and  Paving  Company  are  known  as  No.  2  and  No.  4,  the 
former  being  found  at  the  southeast  end  of  the  so-called  Buck- 


232 


THE  MODERN  ASPHALT  PAVEMENT. 


horn  District,  while  the  No.  4  quarry  or  mine  is  at  the  western  end 
of  the  District  about  1  mile  west  of  Schley  and  7  miles  northeast 
of  Dougherty.  The  composition  of  these  limestones  is  as  follows: 

BITUMINOUS  LIMESTONE  FROM  BUCKHORN  DISTRICT, 
OKLAHOMA. 
TEST  No.  69084. 

LIME    ROCK   NO.    4. 

Bitumen  soluble  in  CS2 4 . 3% 

Carbonates  and  organic  matter 86 . 8 

Mineral  matter  insoluble  in  HC1 8.9 


Extracted  bitumen  penetrates  at  78°  F. . 

LIME    ROCK   NO.    2. 


100.0 
60° 


Test  number                             .... 

69085 

57870 

Bitumen  soluble  in  CS2                

12  1% 

13  1% 

Carbonates  and  organic  matter  

76  5 

81  6 

Mineral  matter  insoluble  in  HC1  

11  4 

5  3 

100.0 

100.0 

Extracted  bitumen  penetrates  at  78°  F.  .  . 

65° 

21° 

In  thin  section  under  the  microscope  it  is  seen  that  these  lime- 
stones differ  entirely  in  their  structure  from  those  found  on  the 
Continent  of  Europe  and  which  have  been  utilized  so  largely  for 
the  construction  of  pavements.  The  mineral  matter  in  the  latter 
consists  entirely  of  the  remains  of  marine  animal  life  that  are  very 
uniformly  impregnated  with  bitumen.  The  limestones  from 
Oklahoma  on  the  other  hand,  contain  a  very  consider- 
able proportion  of  hard  crystalline  calcite  which  is  not  impreg- 
nated at  all  with  bitumen.  On  this  account  the  latter  do  not 
compare  favorably  with  the  rock  asphalts  of  Europe.1 

These  limestones,  as  has  been  said  previously,  have  been  com- 
bined with  the  sand  rock  to  make  a  very  satisfactory  paving  sur- 
face, the  proportions  in  use  being  J  No.  2  lime  rock,  J  No.  4  lime 
rock,  and  J.  sand  rock.  The  sand  rock  supplies  the  flux  necessary 
for  the  hard  bitumen  in  the  limestone,  the  latter  having  a  pene- 

1  See  page  252. 


ASPHALTIC  SANDS  AND  LIMESTONES.  233 

tration  of  only  60  to  65°,  before  heating,  as  it  occurs  in  nature 
and  only  20°  after  that  operation.  Such  a  mixture  has  the  follow- 
ing composition: 

SURFACE  MIXTURE  MADE  FROM  BITUMINOUS  SAND  AND  LIME 

ROCKS  FROM  OKLAHOMA. 

TEST  No.  48231. 

Bitumen  soluble  in  CS2 8.2% 

Passing  200-mesh  sieve 18.8 


100- 
80- 
50- 
40- 
30- 
20- 
10- 


9.0 

18.0 

16.0 

4.0 

3.0 

8.0 

6.0 


Retained  on  10-mesh  sieve 9.0 

100.0 

It  will  be  noticed  that  the  bitumen  in  this  mixture  is  lower 
than  in  a  sand  mixture  of  the  same  grading  and  yet  it  has  been 
shown  by  experience  that  it  is  a  satisfactory  one.  This  is  prob- 
ably due  to  the  fact  that  the  film  of  asphalt  on  the  lime  rock  is 
not  necessarily  as  thick  as  that  upon  the  sand  grains  and  for  this 
reason  the  percentage  of  bitumen  which  this  mineral  aggregate 
will  carry  is  smaller  than  when  the  latter  is  of  a  silicious  nature. 
Although  fairly  satisfactory  pavements  have  been  made  with 
these  materials  it  is  not  probable  that  they  will  prove  of  any  impor- 
tance in  the  paving  industry  as  the  supply  as  turned  out  is  too 
small  to  permit  of  obtaining  a  requisite  quantity  of  uniform  quality 
and  because  the  greatest  skill  is  necessary  in  so  handling  the  mate- 
rial as  to  make  it  possible  to  put  it  down  with  the  bitumen  of  a 
proper  state  of  consistency,  as  this  changes  very  readily  on  being 
heated  in  the  slightest  degree  to  too  high  temperature. 

Bruns)i*ick  District. — The  District  which  has  been  named  by 
Eldridge  the  "  Brunswick  District "  lies  on  the  Brunswick  Creek 
immediately  north  of  Rock  Creek,  to  which  it  is  a  tributary,  4  miles 
northeast  of  Dougherty.  The  deposits  here  resemble  those  found  in 
the  Buckhorn  District.  They  have  been  worked  to  a  certain  extent 
industrially  but  are  probably  of  no  great  commercial  interest. 


234 


THE  MODERN   ASPHALT  PAVEMENT. 


Analyses  of  the  bituminous  products  obtained  there,  made  in 
1898,  resulted  as  follows: 

FROM  BRUNSWICK  DISTRICT,  OKLAHOMA. 

Test  No.  18656  and  18657.    Fossilif  erous  limestone,  impregnated  with  bitumen. 
"      "    18662.     Bituminous  sand,  Kirby  mine. 


'    18667.                                     as  shipped. 
"      "    18668.             "             "      "        " 

Test  number  

18656 
1.6% 

18657 

3.1% 
3.9 
1.0 
1.0 
11.0 
12.0 
30.0 
31.0 
7.0 

18662 

11.3% 
1.7 
29.0 
45.0 
13.0 
0.0 
0.0 
0.0 
0.0 

18667 

9.3% 
1.7 
36.0 
40.0 
13.0 
0.0 
0.0 
0.0 
0.0 

18668 

8.6% 
1.4 
20.0 
42.0 
28.0 
0.0 
0.0 
0.0 
0.0 

Bitumen  soluble  in  CS2 

Passing  200-mesh  sieve  

100-    "        "    

80-    "        "    

50-                   

40-                   

30-                   

20-                   

"         10-                  

100.0 

100.0 

100.0 

100.0 

Materials  received  from  the  same  locality  in   1903  had  the 
following  composition : 


Test  number  

63279 

63280 

63283 

Bitumen  soluble  in  CS2  

4  9% 

6  8% 

2  3% 

Carbonates   .... 

89  1 

86  4 

94  1 

Mineral  matter  insoluble  in  HC1  

6.0 

6.8 

3.6 

100.0 

100.0 

100.0 

REMARKS:  No.  63279.  Hard  compact  limestone  with  free  bitumen  in  small 

seams,  somewhat  crystalline. 

"  63280.  Same  as  No.  63279,  containing  more  seams  and  larger 
ones  and  the  latter  being  filled  with  a  considerable 
seepage  of  free  bitumen,  aside  from  that  impregnat- 
the  rock. 

"  63283.  Same  as  No.  63279,  unevenly  impregnated  with  bitu- 
men, the  seams  carrying  free  material,  although  to 
no  such  extent  as  No.  63280. 

It  would  seem  from  the  above  data  that  there  can  be  no 
question  that  the  lime  rock  will  not  bear  the  cost  of  transportation. 

Arbuckle  Mountains. — Many  deposits  of  bituminous  sands  are 
found  in  the  neighborhood  of  the  Arbuckle  Mountains,  some  of 


ASPHALTIC  SANDS  AND   LIMESTONES.  235 

which  have  been  examined  by  the  author.  That  occurring  south- 
east of  Woodford,  close  to  the  Henryhouse  Creek,  and  known  as 
the  Sneider  Deposit,  has  the  following  composition: 

BITUMINOUS  SAND  FROM    SNEIDER  DEPOSIT,  ARBUCKLE 

MOUNTAINS  DISTRICT,   OKLAHOMA. 

TEST  No.  30478. 

Bitumen  soluble  in  CS2 11 . 1% 

200-mesh  sieve 8.9 

100-    "        "    75.0 

80-    "        " 2.0 


50- 
40- 
30- 
20- 
10- 


2.0 
1.0 
0.0 
0.0 
0.0 


100.0 

The  quarry  is  described  in  detail  by  Eldridge.1 
Attempts  have  been  made  to  extract  the  bitumen  from  this  sand, 
industrially  and  the  material  obtained  has  the  following  properties: 

EXTRACTED  BITUMEN  FROM  BITUMINOUS  SANDS  FROM 

ARBUCKLE    MOUNTAINS  DISTRICT,   OKLAHOMA. 

TEST  No.  30474. 

Loss,  212°  F.,  1  hour 0.1% 

Residue  after  heating  to  212°  F Too  soft  for  pene- 
tration 

DRY   SUBSTANCE. 

Loss,  325°  F.,  7  hours 3.5% 

Residue  after  heating  to  325°  F Penetration  =  110° 

Bitumen  soluble  in  CS2,  air  temperature 68 . 7% 

Difference 1.5 

Inorganic  or  mineral  matter 29 . 8 

100.0 
Malthenes: 

Bitumen  soluble  in  88°  naphtha ,  air  temp.  . .  57 . 3% 

This  is  per  cent  of  total  bituman 83 . 4 

Bitumen  soluble  in  62°  naphtha,  air  temp. . .  62 . 6% 

This  is  per  cent  of  total  bitumen 91.1 

Character  of  extracted  bitumen Soft  at  78°  F. 

The  character  of  this  material  and  the  cost  of  obtaining  it 
will  probably  exclude  it  from  any  commercial  application. 

1  Asphalt  and  Bituminous  Rock  Deposits,  1901,  316. 


236  THE  MODERN  ASPHALT  PAVEMENT. 

The  Elk  Asphalt  Company  has  a  similar  sand  of  the  following 
composition : 

BITUMINOUS  SAND  FROM  ELK    ASPHALT   COMPANY   DEPOSIT, 

OKLAHOMA. 
TEST  No.  30483. 

Bitumen  soluble  in  CS2 8.7% 

Passing  200-mesh  sieve 10 .3 

"       100-    "        "   7.0 

"         80-    "        "   10.0 

"         50-    "        "  34.0 

"         40-    "        "   12.0 

"         30-    "        "   4.0 

"         20-    "        "   4.0 

"         10-    "        "   6.0 

Retained  on  10-mesh  sieve 4.0 


100.0 
Character  of  extracted  bitumen  = Soft  maltha. 

From  this  sand  a  bitumen  has  been  extracted  having  the  follow- 
ing composition: 

BITUMEN  EXTRACTED  FROM  ELK  ASPHALT  COMPANY'S 

DEPOSIT  OF  BITUMINOUS  SAND,  OKLAHOMA. 

TEST  No.  30475. 

Loss,  212°  F.,  1  hour 0.2% 

Consistency  of  residue  after  heating Too  soft  for 

penetration 

DRY   SUBSTANCE. 

Loss,  325°  F.,  7  hours 4.2% 

Consistency  of  residue  after  heating Too  soft  for 

penetration 

Bitumen  soluble  in  CS2,  air  temperature . . .- 88 . 0% 

Difference « 3.1 

Inorganic  or  mineral  matter 8.9 


100.0 
Malthenes : 

Bitumen  soluble  in  88°  naphtha,  air  temperature. . .     79 . 1% 

This  is  per  cent  of  total  bitumen 89 . 9 

Bitumen  soluble  in  62°  naphtha,  air  temperature  .  .     85.4% 
This  is  per  cent  of  total  bitumen 96 . 6 

Extracted  bitumen Too  soft  for 

penetration 


ASPHALTIC  SANDS  AND  LIMESTONES. 


237 


Upon  this  material  the  same  remarks  may  be  made  as  in  the 
case  of  the  Sneider  bitumen. 

Near  Emet,  in  the  same  neighborhood,  bituminous  sands  are 
found  which  have  the  following  characteristics: 

DEPOSIT  OF  BITUMINOUS  SAND  NEAR  EMET,  OKLAHOMA- 
TEST  No.  30477. 

Bitumen  soluble  in  CS2 10.4% 

Passing  200-mesh  sieve 2.6 


100- 
80- 
50- 
40- 
30- 
20- 
10- 


2.0 

5.0 

63.0 

16.0 

1.0 

0.0 

0.0 

100.0 


Consistency  of  extracted  bitumen  = . . .  .  Soft  maltha 

This  sand,  like  the  others,  is  impregnated  with  a  soft  maltha. 

In  the  Quapaw  Reservation  a  sand  occurs  which  contains 
from  16  to  18  per  cent  of  bitumen,  the  sand  grains  having  the 
following  grading : 

BITUMINOUS  SAND,  QUAPAW  RESERVATION,  OKLAHOMA. 


Test  number  

30479 

30141 

Bitumen  soluble  in  CS2  
Passing  200-mesh  sieve.  .  . 

18.0% 
29  0 

16.5% 
37  3 

"       100-    "        "    

12  0 

10  1 

"         80-    "        "    

4  0 

5  0 

"         50-    "        "    

12  0 

19.0 

"         40-    "        "    
"         30-   "        "   
tt         20-    "        "  • 

7.0 
3.0 
2  0 

10.0 

.7 
7 

"         10-    "        " 

4  0 

7 

Retained  on  10-mesh  sieve.  . 

9.0 
100.0 

.0 
100.0 

This  sand  apparently  contains  some  organic  matter  not  of  a 
bituminous  nature. 

Bituminous  Limestone  at  Ravia. — Just  south  of  the  Washita 
River  and  Tishomingo,  at  Ravia,  is  a  large  deposit  of  bituminous 
limestone.  This  contains  7.1  per  cent  of  bitumen  with  varia- 


238 


THE  MODERN  ASPHALT  PAVEMENT. 


tions  between  2.3  and  13.2  per  cent.  The  bitumen  is  a  rather 
dense  maltha  having  a  penetration  of  210°  on  extraction.  The 
limestone  does  not  break  down  on  extraction  with  solvents  and 
in  thin  section  under  the  microscope  is  shown  to  be  of  uneven 
texture  containing  crystals  of  calcite  which  are  not  impregnated 
with  bitumen.  The  rock  is  not  made  up,  as  in  the  case  of  the 
Continental  asphaltic  limestones,  of  the  remains  of  marine  organ- 
isms. Owing  to  this  fact  and  the  small  percentage  of  bitumen 
in  the  rock  it  can  be  of  no  commercial  interest.  Several  samples 
from  the  face  of  the  mine  give  the  following  results  on  analyses: 

BITUMINOUS  LIMESTONE  FROM  RAVIA,  OKLAHOMA. 


Test  number       . 

67316 

67317 

67318 

67319 

67320 

67321 

Bitumen  by  CS2  
Mineral  matter  insoluble 
in  HC1  

10.8% 
18.5 

7.3% 
15  5 

7.0% 
14  3 

3-4% 
30  8 

9.9% 
11  3 

9.6% 
17  9 

Mineral  matter  soluble  in 
HC1     

69.9 

75.8 

73  2 

63  7 

77  9 

71.3 

Difference  

8 

1  4 

5  5 

2  1 

9 

1  2 

100.0 

100.0 

100.0 

100.0 

100.0 

100.0 

The  Ravia  rock  is  typical  of  all  American  asphaltic  limestones 
and  for  this  reason  it  is  hardly  to  be  believed  that  any  of  them 
possess  the  same  desirable  features  as  those  which  are  mined  in 
Europe. 

Other  deposits  in  the  Arbuckle  Mountain  region  are  of  much 
the  same  character  as  those  which  have  been  described  and  are 
of  no  commercial  interest. 

Eldridge  states  that  at  Wheeler  there  is  one  of  the  largest 
oil  seepages  in  the  United  States.  The  character  of  the  maltha 
at  this  point  is  very  much  the  same  as  that  which  has  been  extracted 
from  the  sandstone.  It  is,  of  course,  impossible  to  collect  it  in 
sufficient  quantity  to  be  employed  in  the  paving  industry. 

Five  miles  northwest  of  Ardmore  a  stratum  of  bituminous  sand- 
stone is  found  having  a  dip  which  is  nearly  vertical.  Many  attempts 
have  been  made  to  utilize  this  material  by  boiling  it  with  water, 
but  they  have  all  been  failures  and  have  resulted  in  the  loss  of 
considerable  capital  in  the  same  way  that  has  been  the  case  else- 


ASPHALTIC  SANDS  AND  LIMESTONES. 


239 


where  in  Oklahoma.     The  best  of  the  rock  available  at  this  point 
has  the  following  composition: 

BITUMINOUS  SANDSTONE  NEAR  ARDMORE,  OKLAHOMA. 


47443 

9.6% 
12.4 
50.0 
25.0 
2.0 
1.0 
0.0 
0.0 
0.0 

100.0 

47444 

11.8% 
1.2 
5.0 
16.0 
59.0 
6.0 
1.0 
0.0 
0.0 

100.0 

Bitumen  soluble 
Passing  200-mesl 
100-    " 
80-    " 
50-    " 
40-    " 
30-    " 
20-    " 
"         10-    " 

in  CS2    

ti  sieve   

<  < 

« 

ii 

ti 

it 

ti 

Penetration  of  extracted  bitumen  at  78°  F.  =44°.  Too  soft  for  pen. 
In  the  preparation  of  the  bitumen  by  extraction  it  is  impossible 
to  remove  all  the  fine  material  and  the  maltha  is  much  hardened 
in  the  process  of  boiling  out  the  water.  A  sample  of  the  so-called 
refined  material  contained  77.8  per  cent  of  bitumen  which  had  a 
penetration  of  75°. 

Grahamite  in  Oklahoma. — There  are  several  occurrences 
of  grahamite  in  Oklahoma,  the  chief  one  being  in  what  Eldridge 
has  denominated  the  Tenmile  Creek  District.  This  has  been 
described  in  detail  under  the  heading  "  Grahamite. " 1  At 
another  point,  near  Loco,  in  Section  36,  T.2.S.,  R.4.W.,  gra- 
hamite has  been  found  in  a  network  of  veins  which  is  remarkable 
as  containing  from  23.6  per  cent  to  2.4  per  cent  of  pyrites,  evi- 
dently introduced  by  infiltration.  No  commercial  supply  of 
this  material  is  available. 

Eldridge  has  classified  these  materials  as  "  Asphaltites  "  and 
regards  that  found  at  the  so-called  Moulton  mine  as  closely  resem- 
bling albertite.  He  has  named  it  Impsonite.  The  author  sees 
no  reason  to  use  the  word  Asphaltite  as  applied  to  these  bitu- 
mens as  its  original  use  was  quite  different.  It  is  a  fact  that  the 
weathered  bitumen  at  the  Moulton  deposit  on  the  surface  resembles 
albertite  to  a  considerable  extent,  being  only  slightly  soluble  in 

1  See  page  21L 


240  THE  MODERN  ASPHALT  PAVEMENT. 

the  ordinary  solvents  for  bitumen.  As  the  material  has  been 
taken  out  deeper  down  in  the  vein  it  is  found  to  be  entirely  soluble 
in  carbon  disulphide,  to  yield  a  percentage  of  fixed  carbon  which 
is  characteristic  of  grahamite  and  in  every  way  to  resemble  closely 
the  type  grahamite  originally  described  from  Ritchie  County, 
West  Virginia.  It  cannot,  therefore,  be  properly  assigned  a  new 
name,  Impsonite. 

The  Value  of  the  Deposits  of  Oklahoma  in  Relation 
to  the  Paving  Industry. — From  what  has  been  said  in  our  de- 
scription of  the  Oklahoma  bituminous  deposits  it  is  evident 
that  the  only  conclusion  that  can  be  drawn  in  regard  to  them 
is  that  they  are  of  little  industrial  interest  with  the  exception, 
perhaps,  of  the  grahamite.  The  deposits,  although  large  in  amount, 
taken  as  a  whole  are  individually  small  and  moreover,  far  from 
being  uniform  in  their  character,  they  contain  too  little  bitumen 
and  this  bitumen  is  not  sufficiently  asphaltic  in  its  character. 
It  is  very  improbable  that  any  return  will  ever  be  obtained  for 
the  amount  of  money  that  has  been  spent  in  attempting  to  develop 
them. 

Texas. — Bitumen  is  found  in  Texas  impregnating  limestone  in 
Burnet  and  Uvalde  Counties  and  mixed  with  sand  in  Montague 
County. 

The  latter  deposits  are  near  St.  Jo.  They  are  of  no  commercial 
interest  and  resemble  in  many  respects  those  found  in 
Oklahoma. 

In  Burnet  County,  Eldridge  states,  the  deposit  consists  of 
Cretaceous  limestones  at  Post  Mountain,  near  the  town  of  Bur- 
net,  which  are  impregnated  with  from  4  to  8  per  cent  of  bitumen, 
mostly  with  the  latter  amount.  The  bitumen  is  soft  and  sticky, 
penetrating  240°  on  extraction.  The  quantity  of  asphalt  bearing 
rock  is  stated  to  be  limited. 

In  Uvalde  County  the  bituminous  material  is  found  18  to  25 
miles  west  of  Uvalde  in  the  region  of  the  Anacacho  Mountains. 
The  only  deposit  which  has  been  worked  to  any  considerable 
extent  is  a  peculiar  limestone  which  Eldridge  described  as  being 
"  an  assemblage  of  minute  organisms  together  with  a  conspicuous 
proportion  of  crystalline  calcite.  Molluscan  remains,  often  of 


ASPHALTIC  SA1STDS  AND  LIMESTONES.  241 

large  size,  are  also  present.  Through  the  mass  of  rock  there  is 
a  high  per  cent  of  interstitial  spaces,  which  in  some  instances 
may  even  exceed  the  solid  portions.  In  addition  to  the  inter- 
stitial spaces,  properly  so-called,  are  cavities  produced  by  the 
removal  of  the  molluscan  remains.  .  .  ."  The  bitumen  partially 
fills  these  cavities  and  also  impregnates  the  limestone  to  a  certain 
extent  but  the  voids  are  never  completely  filled.  On  account  of 
the  nature  of  the  rock  and  its  great  lack  of  homogeneity  the  mate- 
rial is  not  satisfactory  for  paving  purposes,  as  is  generally  the 
case  when  calcite  is  present.  The  rock  carries  about  12  to  15  per 
cent  of  a  peculiar  bitumen,  attempts  to  extract  which  were  made 
at  one  tune.  Although  it  is  now  of  no  commercial  value  the 
character  of  the  bitumen  may  be  noted  with  interest. 

AsphaUic  Rock  from  Litho-Carbon  Company. — An  average  sample 
of  the  rock,  Test  No.  7293,  as  worked,  contained  12.8  per  cent  of 
bitumen,  the  mineral  matter  consisting  of  87.0  per  cent  of  lime- 
stone and  1.2  per  cent  of  silicates  insoluble  in  the  acid.  The  bitu- 
men extracted  from  this  had  the  following  characteristics: 

ASPHALTIC  ROCK  FROM  LITHO-CARBON  COMPANY. 

Softens 160°  F. 

Flows 170°  F. 

Per  cent  of  bitumen  soluble  in  88°  naphtha. . .  54 . 5 
Fixed  carbon 18.0 

ULTIMATE    COMPOSITION. 

Carbon 80 . 3% 

Hydrogen 10 . 1 

Sulphur 9.8 

The  character  of  this  bitumen  is  quite  different  from  that  in 
asphalt  found  elsewhere  owing  to  the  fact  that,  notwithstanding 
its  consistency,  it  has  a  high  percentage  of  fixed  carbon  and 
contains  a  larger  amount  of  sulphur  than  is  found  in  any  asphalt 
of  the  same  consistency.  On  account  of  these  peculiar  proper- 
ties it  was  known,  at  the  time  that  an  attempt  was  made  to  put 
it  on  the  market,  as  Litho  Carbon  or  Gum  Asphalt.  There  is, 
of  course,  no  reason  to  call  it  a  gum,  except  from  the  fact  that 
it  might  be  employed  as  a  substitute  for  some  of  the  resins  known 
as  gums  in  the  varnish  trade.  No  native  bitumen  can  possibly 
be  regarded  as  a  gum. 


242 


THE  MODERN  ASPHALT  PAVEMENT. 


A  fine  grained  bituminous  limestone  is  also  found  on  the  Smythe 
Ranch,  "  about  20  miles  a  little  south  of  west  from  Uvalde  and 
4  or  5  miles  south  of  the  quarry  of  the  Uvalde  Asphalt  Company." 
It  is  quite  different  in  character  from  that  which  has  previously 
been  described.  A  specimen  of  the  material  examined  in  the 
author's  laboratory  had  the  following  characteristics: 

BITUMINOUS  LIMESTONE  FROM  SMYTHE  RANCHE,  TEXAS. 
TEST  No.  22070. 

Bitumen  soluble  in  CS2 12.2% 

Limestone 87 . 8 

•     Sand  insoluble  in  HC1. .,    1.2 


100.0 


EXTRACTED    BITUMEN. 


Consistency Hard-friable 

Softens 240°  F. 

Flows 250°  F. 

Fixed  carbon 16 .9% 

Bituminous  sandstones  are  also  found  in  Uvalde  County  and 
consist  of  an  extremely  fine  sand,  the  larger  portion  passing  the 
100-mesh  sieve,  impregnated  with  a  bitumen  yielding  a  large 
amount  of  fixed  carbon  and,  therefore,  similar  to  that  found  in 
the  limestone. 

BITUMINOUS  SANDSTONE,  UVALDE  COUNTY,  TEXAS.  ' 


22071 

22072 

Bitumen  soluble  in  CS2  

9.8% 

8.1% 

Sand  

90.2 

91.9 

Per  cent  of  the  sand  insoluble 
in  HC1  

100.0 
96.5% 

100.0 
93.6% 

Per  cent  of  the  sand  passing- 
100-mesh  sieve  

88.2% 

91.9% 

EXTRACTED    BITUMEN. 

Softens 210°F. 

Flows.  .  ...     220°  F. 


Fixed  carbon 19.5% 


A8PHALTIC  SANDS  AND  LIMESTONES. 


243 


Bituminous  Sands  of  California. — The  location  of  the  bitu- 
minous sands  of  California  has  been  described  in  detail  by  Eld- 
ridge.  It  will  suffice  to  remark  here  upon  the  character  of  some 
of  the  most  important. 

Santa  Cruz  Bituminous  Sands. — The  quarries  of  bituminous 
sand  near  the  summit  of  the  Empire  Ridge,  facing  the  Bay  of 
Monterey  and  the  Pacific  Ocean,  are  of  very  large  extent.  The 
individual  strata  are  very  variable  in  composition,  as  can  be 
seen  from  the  results  of  an  examination  of  the  various  types 
found  there,  collected  by  the  author  in  1898: 

BITUMINOUS  SANDS,  SANTA  CRUZ,  CALIFORNIA, 

Test  No.  13578.  Soft  material  from  the  foot  of  Point  Quarry. 

13579.  Top  of  stratum,  Side  Hill  Quarry. 
"  13580.  Richest  rock,  Side  Hill  Quarry. 

"  13581.  Lowest  stratum,  Rattlesnake  Quarry. 

"  13582.  6  to  9-foot  vein,  Hole  Quarry. 

"  13583.  Poorer  rock,  Hole  Quarry. 

"  13584.  Gray  rock,  Hole  Quarry. 

13585.  6  to  9-foot  vein,  Last  Chance  Quarry. 


Test  number              

13578 

13579 

13580 

13581 

14  4% 

15  4% 

13  2% 

15  1% 

Passing  200-mesh  sieve  

6.4 

5.2 

8.6 

1  5 

100-                   

2.2 

3.4 

5.2 

7  4 

80-                   

10.0 

10.0 

12.0 

10  0 

50-                   

29  0 

30  0 

40  0 

35  0 

40-                  

10  0 

10  0 

13  0 

13  0 

30-                   

15  0 

17  0 

5  0 

10  0 

"         20-                   

9.0 

6.0 

2  0 

5  0 

"         10-                   

4.0 

3.0 

1  0 

3  0 

100.0 

100.0 

100.0 

100.0 

Test  number                        .  . 

13582 

13583 

13584 

13585 

Bitumen  soluble  in  CS2  

17  3% 

11  4% 

11  7% 

14  2% 

Passing  200-mesh  sieve  

5  6 

1  5 

47 

2  4 

100-             "    

24.1 

4.1 

26  6 

2  4 

"         80-             "   

39.0 

12.0 

33  0 

6  0 

"         50-             "   

11.0 

35.0 

20.0 

39  0 

40-              "   . 
"         30-             "   

3.0 
0  0 

20.0 
11  0 

3.0 
1  0 

18.0 
14  0 

"         20-             "   

0.0 

4  0 

0  0 

4  0 

"         10-             "    

0.0 

0.0 

0.0 

0  0 

100.0 

100.0 

100.0 

100.0 

244 


THE  MODERN  ASPHALT  PAVEMENT. 


The  bitumen  which  these  sands  contain  is  in  the  form  of 
maltha,  much  of  it  readily  staining  the  hands  when  the  sands 
are  handled.  It  hardens  on  heating  with  a  loss  oi  the  lighter 
oils  and  a  reduction  in  the  percentage  of  bitumen  to  a  point  which 
makes  it  possible  to  produce  a  surface  mixture  which  will  with- 
stand traffic. 

It  will  be  noted  that  the  grading  of  these  sands  is  sufficiently 
fine  and  that  they  contain  a  certain  amount  of  200-mesh  material. 

The  streets  which  have  been  paved  with  the  Santa  Cruz  bitu- 
minous sands  in  San  Francisco  have  been  only  fairly  satisfactory. 
They  have  required  large  repairs  which,  however,  are  readily  made 
by  reheating  the  material,  but  there  is  now  a  tendency  to  abandon 
this  form  of  asphalt  pavement  and  to  construct  surfaces  from 
properly  graded  sand  combined  with  filler  and  a  suitable  pure 
bitumen. 

San  Luis  Obispo  Bituminous  Sands. — Deposits  of  bituminous 
sands  near  San  Luis  Obispo,  in  the  county  of  the  same  name, 
were  formerly  worked  to  a  very  considerable  extent,  but  these 
sands  were  much  more  variable  in  character  than  those  found  at 
Santa  Cruz.  Different  strata  contain  from  8  to  16  per  cent  of 
bitumen  and  generally  below  10  per  cent.  The  following  analyses 
show  the  characteristics  of  those  which  were  available  in  1898: 

BITUMINOUS  SANDS,  SAN  LUIS  OBISPO,  CALIFORNIA, 


Test  number  

13576 

13577 

Bitumen  soluble  in  CS2.  .  . 
Passing  200-mesh  sieve.  .  . 

8.8% 
11.9 

11.4% 
4.4 

100- 

6.1 

6.1 

80- 

10.2 

16.1 

50- 

50.0 

44.0 

40- 

8.0 

9.6 

30- 

1.0 

5.0 

20- 

_ 

1.0 

3.0 

10- 

3.0 

1.0 

100.0 

100.0 

The  supply  of  the  sands,  which  is  readily  available,  is  now 
nearly  exhausted  and  they  are  no  longer  a  commercial  factor. 


ASPHALTIC  SANDS  AND   LIMESTONES. 


245 


Bituminous  Sands  in  Santa  Barbara  County. — Large  deposits 
of  bituminous  sands  occur  in  Santa  Barbara  County  in  the  Sisquoc 
Hills,  the  location  and  geological  relations  of  which  are  described 
by  Eldridge.1 

The  deposit  worked  by  the  Alcatraz  Company  had  the  following 
composition: 

SANTA  BARBARA  COUNTY,  CALIFORNIA. 


Test  number  

6484 

6485 

Bitumen  soluble  in  CS2 
Passing  200-mesh  sieve 

18.5% 
12.5 

16.5% 
7.5 

. 

100- 

8.0 

7.0 

80- 

3.0 

6.0 

50- 

39.0 

20.0 

40- 

10.0 

20.0 

30- 

8.0 

14.0 

20- 

1.0 

8.0 

10- 

0.0 

1.0 

100.0 

100.0 

This  is  £,  sand  of  medium  grade,  largely  50-  and  40-mesh  grains, 
but  carries  a  very  considerable  amount  of  200-mesh  material. 
The  bitumen  is  in  the  nature  of  a  maltha  and  was  extracted  from 
the  sand  with  naphtha,  sent  down  to  the  seacoast  by  pipe-line 
and  there  recovered  by  distillation.  On  heating,  the  original  soft 
bitumen  was  hardened  to  a  proper  consistency  for  use  for  paving 
purposes.  The  process  proved  to  be  an  expensive  one  and  the 
material  when  extracted  was  of  no  better  quality  than  that  obtained 
by  the  distillation  of  ordinary  California  petroleum.  After  the 
expenditure  of  a  vast  amount  of  money  the  process  was  abandoned. 
Some  of  the  bitumen  prepared  in  this  manner  had  the  following 
characteristics: 

BITUMEN  EXTRACTED  FROM  SANTA  BARBARA  COUNTY, 

CALIFORNIA,   BITUMINOUS  SANDS. 

TEST  No.  35202. 

Penetration  at  78°  F 48° 

Bitumen  soluble  in  CS2,  air  temperature 89.4% 

Difference .3 

Inorganic  or  mineral  matter 10 . 3 


100.0 


The  Asphalt  and  Bituminous  Rock  Deposits,  1901,  429. 


246 


THE  MODERN  ASPHALT  PAVEMENT. 


Carpinteria  Sands. — One  of  the  first  bituminous  sands  to  be 
worked  in  California  for  the  purpose  of  obtaining  a  pure  bitumen 
was  that  known  as  the  Las  Conchas  deposit,  occurring  near  the 
beach  at  Carpinteria,  Santa  Barbara  County.  The  sand  at  this 
point  was  worked  from  the  surface.  It  had  the  following  com- 
position : 

LAS  CONCHAS  DEPOSIT    AT    CARPINTERIA,  SANTA  BARBARA, 

CALIFORNIA. 
TEST  No.  6475. 


Bitumen  soluble  in  CS2  

18.9% 

18.4% 

Passing  200-mesh  sieve  

1.1 

4.5 

100-     '        '     

3.0 

3.0 

80-     ' 

28.0 

25.0 

50-     '        '     

45.2    ' 

48.0 

40-     '        ' 

3  0 

1  1 

30-     '        '     

.8 

.0 

100.0 

100.0 

Per  cent  of  total  bitumen 

soluble  in  88°  naphtha  .... 

83.0% 

Attempts  were  made,  which  were  never  very  successful  prac- 
tically or  commercially,  to  extract  the  bitumen  by  boiling  the 
sand  with  water.  The  material  is  of  interest  to-day  only  his- 
torically and  as  being  typical  of  a  certain  class  of  soft  bitumens 
the  nature  of  which  has  been  already  referred  to  on  page  128. 
They  harden  so  on  heating  that  a  soft  maltha  will  become  con- 
verted into  a  brittle  pitch  most  readily  and  on  this  account  were 
the  cause  of  the  failures  in  the  early  attempts  to  lay  asphalt  sur- 
faces with  California  material. 

The  deposits  of  solid  bitumens  in  California  have  been  con- 
sidered under  the  heading  "  Asphalt." 

Colorado. — The  bitumens  of  Colorado  consist  only  of  a  paraffme 
petroleum,  in  the  Florence  oil  field,  of  some  veins  of  gilsonite 
in  the  western  portion,  and  of  a  grahamite  found  in  Middle  Park, 
the  location  and  manner  of  occurrence  of  the  latter  being  accu- 
rately described  by  Eldridge.  He  speaks  of  it  as  an  asphalt  closely 
resembling  gilsonite  which  is,  of  course,  quite  an  erroneous  descrip- 
tion as  it  does  not  melt  and  yields  47  per  cent  of  fixed  carbon. 
It  has  already  been  described  under  grahamite.1 

1  See  page  2147~ 


ASPHALTIC  SANDS  AND  LIMESTONES. 


247 


The  paraffine  petroleum  furnishes  a  flux  which,  when  carefully 
prepared,  is  entirely  satisfactory  for  use  in  the  asphalt  paving 
industry. 

As  far  as  the  author  is  aware  no  asphaltic  sands  or  limestones 
occur  in  Colorado  which  are  of  commercial  importance. 

The  Gilsonites  and  Other  Solid  Native  Bitumens  of  Utah. — 
Utah  has  deposits  of  bitumen  of  very  varied  character.  Gil- 
sonite  veins  are  characteristic  of  this  state  and  the  material  which 
they  furnish  has  already  been  described.  Wurtzilite  and  Ozo- 
cerite are  found  in  small  amounts  but  are  of  no  importance  to 
the  paving  industry,  nor  is  the  albertite  which  is  found  about  eight 
miles  from  Helper  Station  on  the  Rio  Grande  &  Western  R.R., 
which  Eldridge  has  unfortunately  described  under  the  new  specific 
name  of  Nigrite,  which  is  quite  unnecessary  and  illustrates  the  dupli- 
cation of  names  which  is  common  among  investigators  who  are  not 
widely  acquainted  with  the  materials  which  they  examine.  It  is 
plainly  an  albertite  as  can  be  seen  from  the  following  determinations 
in  comparison  with  some  for  the  type  albertite  found  hi  Nova  Scotia. 

ALBERTITE. 


Test  number  

19187 

7834 

Utah 

Nova  Scotia. 

Color  of  powder  . 

Black 

Black 

Fracture        

Irregular 

Smooth 

Fusibility  

Does  not 

Intumesces 

Specific  gravity,  78°  F./780  F  

intumesce 
1  092 

1  076 

Bitumen  soluble  in  CS    air  temperature 

5  6% 

*t  Q% 

94.2 

<j.y  /O 

94  1 

Inorsanic  or  mineral  matter            

2 

Trace 

Bitumen  yields  on  ignition  : 

37  0% 

29  8% 

1.06% 

1  2% 

Wurtzilite  might  be  a  valuable  material  for  industrial  purposes 
were  it  available  in  commercial  quantities,  but  this  is  not  the  case. 
Ozocerite  could  never  be  of  any  value  to  the  paving  industry 


248 


THE  MODERN  ASPHALT  PAVEMENT 


as  it  is  a  hard  paraffine.     The  location  of  all  these  deposits  are 
closely  fixed  by  Eldridge. 

Bituminous  Sands  and  Limestones. — Asphaltic  limestone  is 
found  in  the  same  geological  horizons  as  those  in  which  the  alber- 
tite  and  wurtzilite  of  Utah  occur  and  its  bitumen  is  probably  of 
the  same  origin.  That  located  by  Eldridge  between  Strawberry 
and  Soldier  creeks,  7  miles  northwest  of  Clear  Creek  Station, 
on  the  Rio  G.  &  W.  R.R.,  is  far  from  uniform  in  composition, 
which  has  been  found  in  the  author's  laboratory  to  be  as  follows: 

ASPHALTIC   LIMESTONE  FROM  NEAR  CLEAR  CREEK 
STATION,  UTAH. 


21633 

21634 

21635 

21636 

Bitumen  soluble  in  CS8     

13.7% 

13.3% 

7.3% 

5.2% 

Penetration  of  extracted  bitumen  at 
78°  F             

10° 

15° 

7° 

10° 

Part  soluble  in  HC1 

62  3% 

58  1% 

52  9% 

64  2% 

The  ignited  residue  effervesces  with  acid. 

A  limited  supply  of  fairly  pure  bitumen  has  been  obtained  from 
this  rock,  which  has  the  characteristics  given  in  the  table  on  page  249. 

This  is  a  most  remarkable  bitumen  since  there  is  such  a  great 
variation  in  the  solubility  in  88°  and  62°  naphthas  and  since  it 
yields  no  fixed  carbon  on  ignition.  From  a  scientific  point  of 
view  it  is  worthy  of  careful  study. 

Eldridge  mentions  deposits  of  asphaltic  limestones  in  the  same 
locality  as  that  in  which  the  wurtzilite  veins  occur  along  por- 
tions of  the  outer  face  of  the  Roan  Plateau,  on  its  westward  exten- 
sion, across  Soldier  Summit.  These  deposits  have  not  been  iden- 
tified as  any  that  have  come  into  the  author's  hands. 

In  Grand  County,  near  the  western  border  of  Colorado,  at 
the  head  of  the  West  Water  Canon,  20  miles  north  of  West  Water, 
free  bitumen  has  been  obtained  to  a  certain  extent,  both  in  soft 
and  hard  form.  This  material  when  examined  in  the  author's 
laboratory  was  found  to  have  the  characteristics  given  in  the  table 
on  page  250,  Test  No.  60532. 


ASPHALTIC  SANDS  AND   LIMESTONES.  249 

BITUMEN  EXTRACTED  FROM  LIMESTONE  ROCK  FOUND 

NEAR  CLEAR  CREEK  STATION,  UTAH. 

TEST  No.  21632. 

Specific  gravity,  78°  F./780  F 1 . 20 

Color Light  brown 

Lustre Dull  shining 

Structure Compact 

Fracture Conchoidal 

Hardness,  original  substance 1 

Fuses Readily 

Softens 210°  F. 

Flows 220°  F. 

Loss,  212°  F.,  1  hour .6% 

Bitumen  soluble  in  CS2,  air  temperature 75 . 3% 

Difference 3.4 

Inorganic  or  mineral  matter. 21.3 

100.0 
Mineral  matter  soluble  in  HC1. 48 .4%       , 

Bitumen  soluble  in  88°  naphtha,  air  temperature 48 . 3% 

This  is  per  cent  of  total  bitumen 64 . 3 

Bitumen  soluble  in  62°  naphtha,  air  temperature 72 . 8% 

This  is  per  cent  of  total  bitumen 96 . 7 

Bitumen  yields  on  ignition: 

Fixed  carbon 0.0% 

Penetration  of  extracted  bitumen  at  78°  F 45° 

From  the  small  percentage  of  fixed  carbon  which  the  Grand 
County  bitumen  yields  it  is  evident  that  it  is  not  a  true  asphalt, 
that  it  approaches  in  composition  more  nearly  that  of  the  paraffine 
series,  and  resembles  to  some  degree  the  material  described  from 
the  locality  near  Clear  Creek  station. 

The  soft  bitumen  found  at  this  point  is  a  maltha  which  is  very 
pure,  98.6  per  cent  of  bitumen,  which  consists  almost  entirely 
of  maHhenes  soluble  in  88°  naphtha,  94.5  per  cent. 

It  has  a  specific  gravity  of  .9874  and  after  heating  for  7  hours 
at  325°  F.  hardens  to  a  consistency  of  53°  and  to  23°  after  the 
same  length  of  time  at  400°  F. 

These  bitumens  are  of  no  commercial,  but  of  great  scientific 
interest  as  they  differ  so  markedly  in  their  characteristics  from. 


250  THE  MODERN  ASPHALT  PAVEMENT. 

other  asphalts.     Gilsonite  may  have  been  derived  from  such  a 
material. 

BITUMEN  FROM  GRAND  COUNTY,  UTAH. 
TEST  No.  60532. 

DRIED    CRUDE. 

Bitumen  soluble  in  CS2,  air  temperature 43 .2% 

Difference 7.5 

Inorganic  or  mineral  matter 49 . 3 


100.0 

EXTRACTED    BITUMEN. 

Specific  gravity,  78°  F./780  F 1 .037 

Color Black 

Hardness Variable 

Odor. Asphaltic 

Softens 203°  F. 

Flows 221°  F. 

Penetration  at  78°  F 22° 

Loss,  212°  F.,1  hour 2.8  % 

Bitumen  soluble  in  CS2,  air  temperature 94 . 8% 

Difference 1.6 

Inorganic  or  mineral  matter 3.6 

100.0 

Bitumen  soluble  in  88°  naphtha,  air  temperature     68 . 7% 
This  is  per  cent  of  total  bitumen 71.0 

Bitumen  soluble  in  62°  naphtha,  air  temperature     90 . 3% 
This  is  per  cent  of  total  bitumen . .     93 . 3 

Bitumen  yields  on  ignition : 

Fixed  carbon.  .  .< 8.0% 

Bituminous  Sands. — Bituminous  sandstones  occur  in  various 
parts  of  Utah.  The  A.  L.  Hobson  mine,  H-  miles  from  Thistle 
Junction,  is  a  material  of  the  following  composition: 

BITUMINOUS  SAND  FROM  A.  L.  HOBSON  MINE,  THISTLE 
JUNCTION,   UTAH. 

TEST  No.  21730. 
Loss,  212°  F.,  until  dry 0.1% 

Bitumen  soluble  in  CS2 11 . 6% 

Part  soluble  in  HC1.  .  .20.0 


ASPHALTIC  SANDS  AND  LIMESTONES.  251 

It  appears  that  this  is  a  mixture  of  sand  and  silicates. 

About  8  miles  from  Sunnyside,  in  Carbon  County,  on  the  Rio 
G.  &.  W.  R.R.,  a  bituminous  sand  is  found  in  large  quantities 
which  has  the  following  composition: 

BITUMINOUS  SAND,  SUNNYSIDE,  CARBON  COUNTY,  UTAH. 
TEST  No.  37048. 

Bitumen  soluble  in  CS2 11 .2% 

Passing  200-mesh  sieve 16 .8 

"       100-    "        "   

"         80-    "        "   

50-    "        "    

"         40-    "        "   

"         30-    "        "    

"         20-    "        "    , 

"         10-    "        "   

100.0 

Mineral  matter Quartz  sand 

Extracted  bitumen Pulls  to  a  thread 

The  mineral  matter  consists  of  quartz  sand  and  the  extracted 
bitumen  possesses  the  characteristics  of  a  maltha. 

In  Whitmore  Canon  bituminous  sandstone  occurs  nearly  free 
from  carbonates,  the  bitumen  having  a  penetration  of  35°.  It 
has  the  following  characteristics: 

BITUMINOUS  SAND,  WHITMORE  CANON,  UTAH. 
TEST  No.  21729. 

Bitumen  soluble  in  CS2. 10.9% 

Passing  200-mesh  sieve 17.9 

"       100-    "        "    16.1 

"         80-    "        "   16.1 

"         50-    "        "    21.4 

"         40-    "        "    14.2 

"         30-    "        "    3.4 

100.0 

Per  cent  soluble  in  HC1 2.6% 

Extracted  bitumen,  penetration  at  78°  F.  =     35° 

The  bitumen  obtained  from  this  sand  is  a  maltha  which  has 
been  examined  by  the  author  with  the  following  results: 


252  THE  MODERN  ASPHALT  PAVEMENT. 


BITUMEN  EXTRACTED  FROM  SAND  FROM  WHITMORE 
CANON,  UTAH. 

TEST  No.  21731. 

Penetration  at  78°  F Too  soft 

for  test 

Loss,  212°  F.,  until  dry 18.6% 

Loss,  325°  F.,  7  hours 6.6% 

Residue  after  325°  F.  penetrates 145° 

Bitumen  soluble  in  CS2,  air  temperature 97 . 8% 

Difference 0.6 

Inorganic  or  mineral  matter 1.6 

100.0 

Bitumen  soluble  in  88°  naphtha,  air  temperature     89.8% 
This  is  per  cent  of  total  bitumen 91 . 8 

Bitumen  soluble  in  62°  naphtha,  air  temperature     97.0% 
This  is  per  cent  of  total  bitumen 98 . 7 

Bitumen  yields  on  ignition : 
Fixed  carbon. 5.0% 

It  is  evident  from  the  small  amount  of  fixed  carbon  which  it 
yields  that  it  is  not  asphaltic  and  it,  therefore,  corresponds  in 
this  respect  with  the  bitumen  found  in  similar  Utah  bituminous 
sands  and  limestones  previously  described.  It  would  seem,  there- 
fore, that  the  bitumens  of  this  nature  found  in  Utah  are  more  closely 
allied  to  ozocerite  or  to  gilsonite  than  they  are  to  the  asphalts. 

Deposits  in  Other  States. — Seepages  of  maltha  and  sand  and 
limestone  impregnated  therewith  are  found  in  many  other  States, 
the  distribution  of  bitumen  being  much  more  general  than  would 
be  supposed.  None  of  these  deposits  are  of  any  commercial  inter- 
est and  must,  therefore,  be  passed  over. 

Continental  Rock  Asphalts. — The  asphaltic  limestones  from 
the  Continent  of  Europe,  which  have  been  the  main  source  of 
the  material  for  the  asphalt  paving  industry  in  that  country, 
are  scattered  through  France,  Switzerland,  Germany,  Sicily,  and 
Italy.  As  these  rocks  reach  the  United  States  they  have  the 
composition  given  on  pages  253  and  254. 


ASPHALTIC  SANDS  AND   LIMESTONES. 


253 


CONTINENTAL  ROCK  ASPHALTS. 

Test  No.  47137.  Ragusa,  Sicily. 

"      "    47147.  Seyssel,  France. 

"      "    47153.  Vorwohle. 

"      "    47156.  Sicula,  Sicily. 

"      "    47159.  Neuchatel,  Val  de  Travere. 

"      "    47162.  Mons. 


Test  number 

47137 

47147 

47153 

47156 

47159 

47162 

Bitumen  soluble  in  CS2  .  . 

9.9% 

5.9% 

7.5% 

10.2% 

9.1% 

8.9% 

Passing  200-mesh  sieve 
100- 

37.1 
17.0 

44.1 
10.0 

18.5 
14.0 

33.8 
16.0 

36.9 
14.0 

53.1 
9.0 

80- 

6.0 

5.0 

21.0 

9.0 

15.0 

4.0 

50- 

14.0 

9.0 

25.0 

18.0 

14.0 

7.0 

40- 

4.0 

7.0 

7.0 

8.0 

4.0 

5.0 

30-               < 

2.0 

7.0 

2.0 

3.0 

4.0 

3.0 

20-             "        . 

5.0 

6.0 

3.0 

1.0 

2.0 

5.0 

a         10_    a        « 

5.0 

6.0 

2.0 

1.0 

1.0 

5.0 

100.0 

100.0 

100.0 

100.0 

100.0 

100.0 

For  some  of  the  rocks  which  have  not  been  examined  by  the 
author  reference  must  be  made  to  the  analyses  of  others.1  See 
the  table  on  page  254. 

These  asphaltic  limestones  are  characterized  more  by  differences 
in  the  grain  of  the  limestone  than  of  their  bitumen  contents.  As 
seen  in  thin  sections  it  appears  that  the  Continental  asphaltic  lime- 
stones consist  of  the  remains  of  marine  animal  life,  and  it  is 
undoubtedly  this  fact  which  gives  them  their  uniform  impregna- 
tion and  their  faculty  of  being  readily  compacted,  as  distinguished 
from  American  asphaltic  limestones  which  contain  very  con- 
siderable proportions  of  hard  crystalline  calcite  not  impregnated 
with  bitumen. 

The  Sicilian  rock  may  vary  in  bitumen  from  6.6  to  11.4  per 
cent.  The  rock  exported  by  the  Sicula  Company  is  about  as  rich — 
3000  tons  examined  by  the  author,  in  three  samples,  containing 
9.5,  9.3,  and  9.9  per  cent  of  bitumen,  though  some  of  it  reaches 
12  per  cent.  The  Mons  rock  is  not  evenly  impregnated;  veins 
which  are  pure  white  being  scattered  through  the  material.  This 
rock  is  used  more  on  account  of  the  character  of  the  grain  than 

1  Dietrich,  Die  Asphaltenstrassen. 


254 


THE  MODERN  ASPHALT  PAVEMENT. 


for  its  bitumen  contents,  which  will  average  6.5  per  cent  to  9.0*per 
cent.  The  rock  obtained  from  the  Seyssel  mine  at  present  is  very 
poor  in  bitumen,  not  exceeding  6  per  cent  and  in  some  cases  drop- 
ping to  1  per  cent.  It  is  used  on  account  of  the  character  of  the 
grain  of  the  stone. 

CONTINENTAL  ROCK  ASPHALTS. 

1.  Val  de  Travers.  5.  Cesi. 

2.  Seyssel,  Pyrimont.  6.  Roccamorice. 

3.  Lobsann.  7.  Limmer. 

4.  Ragusa.  8.  Vorwohle. 


1 
10.15% 

2 

8  15% 

3 

12  32% 

4 

8  92% 

88.40 

91.30 

71  43 

88*21 

0.25 

0.15 

5  91 

0  91 

5.18 

Carbonate  of  magnesia  

6.30 

0.10 

0.31 

0  96 

Sand                     •••  

3  15 

0  60 

Insoluble  in  acid   

6.45 

0.10 

0.45 

0.20 

1  70 

0  40 

5 

7.15% 

6 

12.46% 

7 
14  .  30% 

8 
8.50% 

Carbonate  of  lime   

73.76 

77  53 

67  00 

80  04 

1.72 

2  63 

Alumina  and  iron  oxides  

3.02 

2.17 

1    A 

j  4.  03 

Carbonate  of  magnesia  

14.24 

4.71 

17  52 

0.55 

Sand                          

0  10 

0  50 

1   A    m 

Insoluble  in  acid     

J4.77 

Difference     

1  18 

2.11 

The  richer  Sicilian  rock  by  itself  does  not  form  a  stable  pave- 
ment but  when  some  of  the  Seyssel  or  Mons  rock  is  added  to  it 
stability  is  obtained. 

Continental  rock  asphalts  are  now  used  in  this  country  almost 
solely  in  mastics,  the  extreme  slipperiness  of  the  pavement  made 
with  them  having  proved  so  objectionable  in  comparison  with 
the  asphaltic  sand  pavements  that  the  former  are  no  longer  toler- 
ated. 


ASPHALTIC  SANDS  AND  LIMESTONEa  255 

SUMMARY. 

The  asphaltic  sands  and  limestones  of  the  United  States  have 
not  been  shown  to  be  attractive  to  those  interested  in  the  con- 
struction of  asphalt  pavements.  The  asphaltic  sands  of  Kentucky 
are  too  deficient  in  bitumen  to  make  a  satisfactory  surface  mix- 
ture and  at  the  same  time  the  character  of  the  bitumen  which 
they  contain  is  altogether  too  oily.  Successful  surfaces  have  never 
been  made  with  these  materials  unless  they  have  been  largely 
amended  by  the  addition  of  a  considerable  amount  of  a  harder 
bitumen  and  a  proper  proportion  of  filler. 

The  bituminous  sands  of  California,  although  they  have  been 
used  to  a  very  considerable  extent,  are  now  known  to  give  results 
which  cannot  compare  favorably  in  any  way  with  the  artificial 
mixtures  which  have  been  laid  along  parallel  streets.  Their  use 
for  heavy  traffic  work  will  no  doubt  be  soon  abandoned. 

The  bituminous  limestones  and  sands  of  Oklahoma 
occur  in  such  small  masses  and  pockets  that  their  uniformity 
can  never  be  guaranteed.  In  a  few  instances  excellent  street 
surfaces  have  been  constructed  from  the  mixed  sands  and  lime- 
stones obtained  near  Dougherty,  but  the  character  of  the  asphaltic 
limestones  is  such  that  they  can  never  be  used  in  the  same  way 
as  the  Continental  asphaltic  limestones,  owing  to  the  structure 
of  their  mineral  aggregate. 

As  a  whole  it  is  probable  that  more  money  has  been  lost  hi 
attempting  to  develop  the  isphaltic  deposits  described  in  this 
chapter  than  will  ever  be  recovered  by  working  them. 


CHAPTER  XIII. 

RESIDUAL   PITCHES,  OR  SOLID  BITUMENS  DERIVED  FROM 
ASPHALTIC  AND   OTHER  PETROLEUMS. 

IF  the  distillation  of  the  asphaltic  petroleums  of  California, 
of  the  semi-asphaltic  petroleums  of  Texas,  or  even  of  Russian  oil 
and  some  paraffine  petroleums,  is  carried  sufficiently  far  the  residue 
on  cooling  will  be  found  to  be  a  solid  bitumen,  and  from  asphaltic 
oils  of  a  more  or  less  asphaltic  nature.  The  properties  of  these 
solid  bitumens  and  their  availability  for  industrial  purposes  depend 
largely,  of  course  on  the  nature  of  the  petroleum  from  which 
they  are  derived,  the  care  with  which  the  distillation  is  conducted 
and  the  amount  of  cracking  which  has  taken  place  in  the  process. 

Residual  Pitches  from  California  Petroleum. — The  residues 
from  California  petroleum  have  been  used  to  a  very  consider- 
able extent  in  the  paving  industry  and  are  generally  known  as 
"  D  "  grade  asphalt  or  under  some  trade  designation  or  brand, 
such  as  Diamond,  Obispo,  Acme,  or  Hercules. 

They  have  been,  usually,  all  moreor  less  carelessly  manufactured 
without  laboratory  control  and  consequently  vary  in  character  and 
consistency.  As  a  rule  they  are  by-products  resulting  from  the 
recovery  of  distillates  of  different  gravities  from  crude  petroleum 
and  are  not  prepared  especially  for  paving  purposes.  That 
they  are  badly  cracked  in  the  process  of  manufacture,  the  oil 
often  being  heated  as  high  as  900°  F.,  appears  from  the  fact  that 
if  the  petroleum  from  which  they  are  obtained  is  distilled  or  evap- 
orated under  such  conditions  that  cracking  will  not  occur,  as 
much  as  60  per  cent  of  a  hard  residue  will  remain,  as  shown  by 
the  following  figures  obtained  in  the  author's  laboratory,  as  com- 
pared with  30  per  cent  by  industrial  methods. 

256 


RESIDUAL  PITCHES.  257 

RESIDUAL  PITCH  FROM  CALIFORNIA  PETROLEUM  PREPARED 
IX  THE  LABORATORY. 

TEST  No.  69209. 

Loss,  212°  F  ,  to  constant  weight 2.8% 

Loss,  heating  until  59°  penetration  is  obtained. ...  38 . 9% 

Residual  solid  bitumen  penetrating  59°. 61 . 1 

100.0 

ANALYSIS   OF   BITUMEN   PENETRATING   59°. 

Loss,  400°  F.,  4  hours 4.5% 

Penetration  of  residue  after  heating 29° 

Bitumen  soluble  in  CS2,  air  temperature 99.8% 

Difference 1 

Inorganic  or  mineral  matter. 1 

100.0 
Malthenes: 

Bitumen  soluble  in  88°  naphtha,  air  temperature    77 . 6% 
This  is  per  cent  of  total  bitumen 77.8% 

Carbenes : 

Bitumen  insoluble  in  carbon  tetrachloride,  air 

temperature. , 0.5% 

Bitumen  yields  on  ignition: 

Fixed  carbon 10.5% 

As  a  matter  of  fact,  under  the  conditions  which  obtain  indus- 
trially, only  30  to  40  per  cent  of  solid  residue  is  recovered,  the 
remainder  being  cracked  and  volatilized,  and  such  residues  con- 
tain a  much  larger  amount  of  fixed  carbon,  15  to  20  per  cent,  than 
is  found  on  careful  evaporation.  With  the  form  of  still  at  present 
in  use  and  with  the  most  careful  handling  the  temperature  rises 
to  720°  F.  and  tho  residual  pitch  is  much  smaller  in  amount,  in 
the  author's  experience,  than  it  should  be.  As  an  illustration 
of  this,  at  an  oil  works  under  the  author's  observation,  where 
an  endeavor  was  made  to  produce  the  best  "  D  "  grade  material 
for  paving  purposes,  the  petroleum  in  use,  on  careful  evaporation 
at  400°  F.,  left  a  residuum  of  solid  bitumen  amounting  to  61.1  per 
cent,  and  penetrating  59°,  as  appears  in  the  preceding  table,  whereas 
industrially  only  33  per  cent  was  recovered  having  about  the  same 
penetration.  The  physical  characteristics  and  proximate  com- 
position of  the  industrial  product  obtained  in  this  way  are  given 
in  the  accompanying  tables.  See  pages  258,  259, 260, 261 ,  and  262. 


258 


THE  MODERN  ASPHALT  PAVEMENT. 

"DEGRADE    CALIFORNIA    ASPHALT— PHYSICAT 


Test  number 18250 

Year  received 1898 

PHYSICAL   PROPERTIES. 

Specific  gravity  78°  F./780  F.,  original  substance,  dry 1 .089 

Color  of  powder  or  streak Black 

Lustre Lustrous 

Structure Uniform 

Fracture '. Conchoidal 

Hardness,  original  substance —  1 

Odor Asphaltic 

Softens 150°  F. 

Flows 162°  F. 

Penetration  at  78°  F 25° 

CHEMICAL   CHARACTERISTICS. 

Loss,  325°  F.,  7  hours .83% 

Residue  penetrates  at  78°  F 17° 

Loss,  400°  F.,  7  hours  (fresh  sample) 4.9% 

Residue  penetrates  at  78°  F ., 9° 

Bitumen  soluble  in  CS2,  air  temperature 98 . 3% 

Difference  . 0.5 

Inorganic  or  mineral  matter 1.2 

100.0 

Malthenes : 

Bitumen  soluble  in  88°  naphtha,  air  temperature 65 .0% 

This  is  per  cent  of  total  bitumen. 68 . 6 

Per  cent  of  soluble  bitumen  removed  by  H,jSO4 50.0 

Per  cent  of  total  bitumen  as  saturated  hydrocarbons 33 . 1 

Carbenes : 

Bitumen  insoluble  in  carbon  tetrachloride,  air  tempera- 
ture   7.0 

Bitumen  yields  on  ignition: 

Fixed  carbon 19.0% 


It  will  be  noted  by  a  comparison  of  the  above  data  with 
those  given  on  page  257  that  while  the  solubility  of  the  bitumen 
in  carbon  disulphide  is  unaltered  in  the  process  of  distillation  a 
very  considerable  portion  of  it  has  often  been  rendered  insoluble 
in  cold  carbon  tetrachloride  and  in  88°  naphtha.  At  the  same 
time  the  amount  of  fixed  carbon  in  the  industrial  product  is  largely 


RESIDUAL  PITCHES. 
CHARACTERISTICS   AND  PROXIMATE  COMPOSITION. 


259 


68488 

69549 

69550 

69605 

69606 

1903 

March  1904 

March  1904 

April  1904 

April  1904 

1.062 
Black 
Lustrous 
Uniform 
Sticky 
Tacky 
Asphaltic 
142°  F 
156°  F. 
52° 

1.052 
Black 
Lustrous 
Uniform 
Sticky 
Tacky 
Asphaltic 
178°  F. 
190°  F. 
45° 

1.046 
Black 
Lustrous 
Uniform 
Sticky 
Tacky 
Asphaltic 
106°  F. 
120°  F. 
65° 

1.055 
Black 
Lustrous 
Uniform 
Sticky 
Tacky 
Asphaltic 
128°  F. 
141°  F. 
50° 

1.071 
Black 
Lustrous 
Uniform 
Conchoidal 
-1 
Asphaltic 
120°  F. 
135°  F. 
52° 

83% 
Hard 

H'&S6 

r  3^% 

2.1% 
23° 

2.7% 
29° 

Hard° 

9.6% 
Hard 

to4% 

6-7% 
10° 

7.1% 
16° 

99.3% 
!3 

99.2% 
.8 
Trace 

99.6% 

!o 

99.6% 
.3 
.1 

99.7% 
.3 
Trace 

100.0 

100.0 

100.0 

100.0 

100.0 

77.0% 
77.5 
47.8 
40.5 

66.6% 
67.0 
56.9 
28.9 

70.5% 
70.8 
62.7 
26.4 

68.5% 
68.8 
57.7 
29.2 

•  £8* 

57.3 

42.8 

0.5% 

7.3% 

2.8% 

2.2% 

6.0% 

15.0% 

18.0% 

16.7% 

18.0% 

18.8% 

increased  and  this  increase  corresponds  to  the  degree  of  severity 
of  the  heat  to  which  the  oil  has  been  subjected.  These  differ- 
ences characterize  the  California  pitches  as  being,  to  a  certain 
extent,  products  of  decomposition  and  on  this  account  undesirable 
material. 

Considered  as  a  class  they  are  also  undesirable  because  they 


260 


THE  MODERN  ASPHALT  PAVEMENT. 
"D"  GRADE  CALIFORNIA  ASPHALT. 


18250 

Carelessly 
Prepared 

1.089 
Black 
Lustrous 
Uniform 
Conchoidal 
-1 
Asphaltic 
150°  F. 
162°  F. 
25° 

•  83% 
17° 

4.9% 
9° 

98.3% 
0.5 
1.2 

100.0 

65.0% 
68.6 

50.0 
33.1 

68488 
More 
Carefully 
Prepared 

1.062 
Black 
Lustrous 
Uniform 
Tacky 
Sticky 
Asphaltic 
142°  F. 
156°  F. 
52° 

Hf?d% 

£? 

99.3% 
!3 
100.0 

77.0% 
77.5 

47.8 
40.5 

80.2% 
80.8 

0.5% 
15.0% 

PHYSICAL    PROPERTIES. 

Specific  Gravity,  78°  F./780  F.,  original  sub- 
stance    dry                            

Odor                               

Softens.  .               .    

Flows  .,  

Penetration  at  78°  F  

CHEMICAL    CHARACTERISTICS. 

Dry  substance: 
Loss  325°  F    7  hours       

Loss  400°  F.,  7  hours  (fresh  sample)  

Residue  penetrates  at  78°  F  

Bitumen  soluble  in  CS2  air  temperature  

Malthenes: 
Bitumen  soluble  in  88°  naphtha,  air  tern- 
perature                                       

This  is  per  cent  of  total  bitumen  

Per  cent  of  soluble  bitumen   removed  by 
H  SO                             

Per  cent  of  total  bitumen  as  saturated  hy- 

Bitumen  soluble  in  62°  naphtha  

Carbenes: 
Per  cent  of  bitumen  insoluble  in  carbon 
tetrachloride  air  temperature 

7.0% 
19.0% 

Bitumen  yields  on  ignition: 

RESIDUAL  PITCHES. 


261 


are  not  uniform  in  character,  as  shown  by  the  different  degree 
of  solubility  of  the  bitumen  in  cold  carbon  tetrachloride  and  by 
the  very  considerable  variation  in  the  amount  of  fixed  carbon 
which  they  yield. 

"D"  GRADE  ASPHALT  FROM  REFINERY  AT  LOS  ANGELES,  CAL. 
AVERAGE  AND  EXTREMES  OF  COMPOSITION  IN  1904. 


Average. 

Highest. 

Lowest. 

PHYSICAL    PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original  sub- 

1  060 

1  066 

1  054 

Flashes,  °  F  ,  N  Y.  State  oil-tester  

406°  F. 

420°  F. 

385°  F. 

Softens  

137°  F. 

190°  F. 

124°  F. 

Flows 

150°  F. 

180°  F. 

140°  F 

Penetration  at  78°  F  .  .  .             

56° 

118° 

24° 

CHEMICAL   CHARACTERISTICS. 

Loss  400°  F    4  hours.                  

7.12% 

9.40% 

5  52% 

Residue  after  heating  penetrates  at  78°  F..  .  . 

Bitumen  soluble  in  CSa,  air  temperature  .... 
1  hfterence  ."  

14° 

99.4% 
.4 

15° 

99.9% 
1.59 

12° 

98.1% 
.0 

Inorganic  or  mineral  matter  

2 

.54 

o 

Malthenes: 
Per  cent  of  total  bitumen  soluble  in  88° 
naphtha  air  temperature             ... 

100.0 
71  61% 

83  81% 

66  01% 

Carbenes  : 
Insoluble  in  carbon  tetrachloride,  air  tern- 

4.37% 

6.91% 

32% 

565 

From  an  average  of  a  very  large  number  of  analyses  of  "  D  " 
grade  asphalts  it  has  been  found  that  the  amount  of  fixed  carbon 
which  they  yield,  when  prepared  as  carefully  as  possible  by  the 
present  industrial  process,  does  not  vary  far  from  15  per  cent, 
although  at  times  it  reaches  19  per  cent  where  the  product  is  care- 
lessly handled,  and  should  not  exceed  10  per  cent  as  shown  by 
our  laboratory  results.  This  characteristic  of  the  California 
pitches  is  important  in  differentiating  them  from  those  made 


262 


THE  MODERN  ASPHALT  PAVEMENT. 


from  Texas  oil,  which  yield  a  much  higher  percentage  of  fixed 
carbon. 

"D"  GRADE  CALIFORNIA  ASPHALT.    BITUMEN  INSOLUBLE  IN 
CARBON  TETRACHLORIDE. 


Test  Number. 

Bitumen  Insolu- 
ble in  Carbon 
Tetrachloride, 
Air  Temperature. 

18250 

7.0% 

63847 

.5 

69549 

7.3 

73798 

.6 

73799 

.4 

73800 

.3 

73801 

.1 

73959 

.2 

73960 

.1 

73961 

.1 

73962 

.2 

74087 

.2 

74088 

2.8 

74089 

.1 

74090 

.2 

74091 

1.3 

For  the  purpose  of  preparing  a  pitch  suitable  for  paving  pur- 
poses it  is,  of  course,  desirable  that  some  of  the  malthenes  should 
be  converted  to  asphaltenes,  although  not  to  carbenes.  The  bitu- 
men, soluble  in  88°  naphtha,  should  be  reduced  to  about  70-75 
per  cent  and  the  fixed  carbon  should  reach  15  per  cent. 

Harder  Residual  Pitches. — Where  the  consistency  of  the 
asphaltic  residue  is  harder,  its  character  has  been  denominated 
by  other  letters  than  "  D."  For  example,  A,  B,  and  C  grades 
are  found,  and  much  of  the  "  D  "  grade  put  upon  the  market 
corresponds  to  these  materials  rather  than  to  a  true  "  D  "  grade. 
Where  an  attempt  is  made  to  manufacture  the  different  grades 
they  are  expected  to  be  of  a  consistency  corresponding  to  the 
following  penetrations  on  the  Bo  wen  scale: 

A  Grade 9° 

B      "    15° 

C       "     25° 

D      " 46°  and  above. 


RESIDUAL  PITCHES.  263 

Residual  bitumens  having  a  penetration  of  less  than  46°  are 
deficient  in  the  less  viscous  malthenes  and  require  a  very  large 
amount  of  flux,  to  bring  them  to  a  proper  consistency  for  paving 
cement.  This  results  in  the  presence  of  too  large  a  percentage 
of  both  brittle  asphaltenes  and  the  lighter  forms  of  malthenes. 
Where  these  very  hard  residual  pitches  are  in  use  in  the  produc- 
tion of  a  paving  cement  the  results  have  been  disastrous  in  climates 
where  severe  conditions  are  met,  although  they  may  be  passable 
in  the  climate  of  Southern  California. 

Of  late  years,  the  use  of  such  very  hard  residual  pitches  has 
been  done  away  with,  and  those  which  are  used  for  paving  purposes 
are  now  very  skilfully  prepared  at  low  temperatures,  of  very  nearly 
the  proper  consistency  for  use  as  a  paving  cement,  so  that  it  is 
not  necessary  to  add  more  than  two  or  three  pounds  of  flux,  and 
often  none  at  all,  before  using  the  bitumen. 

"  Specifications  f or  '  D  '  Grade  Asphalt. — '  D  '  grade  asphalt 
should  be  the  residue  from  the  careful  distillation,  with  steam 
agitation,  of  some  suitable  California  petroleum  at  as  low  a  tem- 
perature as  possible  and  certainly  not  exceeding  700°  F.  It  shall 
be  free  from  free  carbon  or  suspended  insoluble  matter,  which 
are  evidences  of  excessive  cracking. 

"  It  shall  be  soluble  to  the  extent  of  at  least  98  per  cent  in 
carbon  disulphide,  95  per  cent  in  cold  carbon  tetrachloride  and 
not  less  than  65  nor  more  than  80  per  cent  of  it  shall  be  solu- 
ble in  88°  Pennsylvania  naphtha,  preferably  nearer  the  former 
figure. 

"  It  shall  not  flash  below  450°  F.  and  shall  have  a  density  be- 
tween 1.04  and  1.06.  It  shall  not  volatilize  more  than  8.0  per  cent 
at  400°  F.  in  4  hours,  and  shall  have  a  penetration  between  40q 
and  70°.  It  shall  melt  at  not  less  than  140°  nor  over  180°  F.  on 
mercury,  according  to  the  method  in  use  in  the  New  York  Test- 
ing Laboratory,  and  shall  yield  not  more  than  15  per  cent  of 
fixed  carbon  on  ignition. 

"  It  shall  have  a  consistency  of  not  less  than  four  (4)  milli- 
meters penetration  at  78°  F.  when  tested  for  five  (5)  seconds  with 
a  No.  2  needle  weighted  with  100  grams." 

The  lower  the  temperature  at  which  the  asphalt  is  produced 
the  smaller  the  percentage  of  cracked  products  it  will  contain 
and  the  smaller  the  loss  will  be  on  heating  for  4  hours  at  400°  F. 


264 


THE  MODERN  ASPHALT  PAVEMENT. 


The  difference  in  its  character  when  run  down  in  20  and  65  hours 
can  be  seen  from  the  following  figures: 

COMPARISON    BETWEEN    "D"    GRADE   TAKING   65   AND    20 
HOURS  TO  COME  TO  GRADE. 


20 

65 

Still                                     

Small 

Large 

99.65% 

99.90% 

.25 

.10 

Inorganic  or  mineral  matter.  ..    

.10 

00 

Malthenes: 
Bitumen  solution  in  88°  naphtha,  air  temp  
This  is  per  cent  of  total  bitumen 

100.00 

71.77% 
72  02 

100.00 

72.50% 
72  57 

Penetration  of  still  sample  at  78°  F  

70° 

66° 

'*         "  barrelling  sample  at  78°  F  

70° 

69° 

Specific  gravity  78°  F./780  F  

1.057 

1  054 

Softens  

120°  F. 

124°  F. 

Flows  

138°  F. 

140°  F. 

Loss,  400°  F.,  4  hours. 
Penetration,  at  78°  F.,  of  residue  after  heating  .  . 
Yield  

9.4% 
12° 
33  0% 

6.8% 
15° 
43  5% 

For  comparison  with  the  preceding  "  D  "  grade  product  a 
bitumen  procured  on  the  market  in  Los  Angeles,  Cal.,  in  1904, 
will  serve.  See  table  on  page  265. 

Here  the  percentage  of  fixed  carbon  is  very  high  and  that  of 
the  malthenes  is  low,  the  total  bitumen  at  the  same  time  amount- 
ing to  only  93  per  cent,  while  a  very  large  proportion  of  bitumen 
soluble  in  carbon  disulphide  but  insoluble  in  cold  carbon  tetra- 
chloride  and  of  free  carbon  are  present.  This  material  has  been 
plainly  overheated  and  it  will  require  from  30  to  40  pounds  of  flux 
instead  of  the  much  smaller  quantity  necessary  with  a  properly 
prepared  asphalt.  In  this  connection  it  may  be  of  interest  to 
remark  that  the  hardness  of  a  "  D  "  grade  asphalt  is  proportional, 
as  in  the  native  bitumens,  to  the  percentage  of  naphtha  soluble 
bitumen  which  it  contains  as  appears  from  the  following  deter- 


RESIDUAL  PITCHEa 


265 


"D"  GRADE  ASPHALT  FROM  AN  ASPHALTUM  OIL  AND 
REFINING  CO. 

PHYSICAL    PROPERTIES. 

Test  number 69014 

Specific  gravity,  78°  F./780  F.,  original  substance,  dry 1 .077 

Softens 195°  F. 

Flows 205°  F. 

Penetration  at  78°  F 27° 

CHEMICAL   CHARACTERISTICS. 

Original  substance: 

Loss,  212°  F. ,  1  hour * 0.0% 

Dry  substance: 

Loss,  325°  F. ,  7  hours 1.3% 

Character  of  residue Surface 

smooth. 

Loss,  400°  F.,  7  hours,  additional  loas. 5.3% 

Character  of  residue Shrivelled 

surface, 
penetration 
5°. 

Bitumen  soluble  in  CS,,  air  temperature 92 .6% 

Difference  (largely  carbon) 7.3 

Inorganic  or  mineral  matter .1 

100.0 
Malthenes: 

Bitumen  soluble  in  88°  naphtha,  air  temperature 64 . 4% 

This  is  per  cent  of  total  bitumen 69 . 5 

Bitumen  soluble  in  62°  naphtha 65 . 6% 

This  is  per  cent  of  total  bitumen 70 . 8 

Carbenes : 

Bitumen  insoluble  in  carbon  tetrachloride,  air  temperature          13.1% 

Bitumen  yields  on  ignition: 

Fixed  carbon 19 .0% 

REMARKS:    A  small  amount  of  suspended  matter  is  noted  under  the 
microscope. 


266 


THE  MODERN  ASPHALT  PAVEMENT. 


minations  on  the  products  produced  at  one  plant  under  the  same 
conditions : 


Number  

103 

104 

105 

106 

Penetration  at  78°  F  

31° 

53° 

54° 

87° 

Naphtha  soluble  bitumen.  .  . 

66.0% 

70.6% 

70.6% 

72.4% 

Asphaltic  Residues  from  Texas  Oil. — The  semi-asphaltic  oil 
from  the  Beaumont  field  in  Texas  leaves  a  residue  of  solid  bitu- 
men on  distillation  which,  however,  as  in  the  case  of  California 
oil,  varies  in  character  according  to  the  method  of  distillation 
employed.  In  the  case  of  California  oils,  with  careful  distillation 
a  larger  percentage  of  residue  was  obtained  than  was  the  case  indus- 
trially. With  the  Beaumont  oil  the  reverse  is  the  case;  on  dis- 
tillation in  vacuo  but  9.0  per  cent  of  solid  bitumen  was  recovered 
while  industrially  as  much  as  30  per  cent  is  obtained.  This  is, 
probably,  due  to  the  fact  that  condensation  goes  on  in  the  case 
of  the  Beaumont  oil  instead  of  cracking  as  in  the  case  of  California 
petroleum.  Analyses  of  residual  pitches  from  Texas  petroleum 
representing  the  product  as  turned  out  in  1903  and  again  in 
1907,  are  given  on  the  opposite  page,  the  two  materials  originat- 
ing from  different  manufacturers. 

An  examination  of  the  preceding  results  shows  that  the  dis- 
tillation has  been  carried  much  further  than  is  the  case  in  the 
production  of  the  California  asphalts.  This  is  evidenced  by  the 
greater  density  of  the  product  and  the  very  much  higher  per- 
centage of  fixed  carbon  which  it  yields.  It  should  also  be  noted 
that  the  two  forms  of  residual  pitch  are  differentiated  by  the  fact 
that  that  from  the  Texas  oil  contains  a  larger  percentage  of  satu- 
rated hydrocarbons  than  that  from  the  California  oil,  a  fact  which 
might  be  expected  as  the  stability  of  the  former  is  much  greater 
than  that  of  the  latter,  owing  to  the  amount  of  paraffine  hydro- 
carbons which  it  contains.  The  asphaltic  residue  from  the  Texas 
oil  is  marked  by  the  presence  of  a  little  over  1  per  cent  of  paraffine 
scale,  but  the  amount  is  insufficient  to  give  it  the  character  of  a 
paraffine  material. 

The  residual  pitches  from  Texas  oil  are  no  more  uniform  in 


RESIDUAL    PITCHES. 


267 


RESIDUAL  PITCH  FROM  TEXAS  PETROLEUM. 


1903 
68943 

1907 
102529 

PHYSICAL    PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original  sub- 
stance  dry     

1.0803 

1.0703 

Black 

Black 

Lustrous 

Lustrous- 

Uniform 

Uniform 

Semi-conchoidal 

Conchoidal 

-1 

—  1 

Odor                 

Asphaltic 

Petroleum 

Softens      

230°  F. 

143°  F. 

Flows            

247°  F. 

164°  F. 

Penetration  at  78°  F  ,  Bo  wen  

13° 

18° 

Penetrometer  at  78°  F  

7° 

CHEMICAL  CHARACTERISTICS. 

Dry  substance: 
Loss  325°  F  ,  7  hours  

.13% 

95% 

Loss  400°  F.,  7  hours  

.19 

iSr 

Bitumen  soluble  in  CSj,  air  temperature  .  .  . 
Inorganic  or  mineral  matter  

99.0% 

98.2% 
Trace 

Difference      •              •••  

.8 

1.8 

Malthenes: 
Bitumen  soluble  hi  88°  naphtha,  ah-  temp. 
This  is  per  cent  of  total  bitumen  

100.0 

65.4% 
66.1 

100.0 

69.6% 
70  9 

Per  cent  of  soluble  bitumen  removed  by 
H2SO4      .           

32.1 

51.1 

Per  cent  of  total  bitumen  as  saturated 
Hydrocarbons      .                        .... 

44  8 

65  6 

Bitumen  soluble  in  62°  naphtha  

71.5% 

70  1% 

72.2 

7i:4 

Carbenes: 
Bitumen  insoluble  in  carbon  tetrachloride, 

5.1% 

14.6% 

Bitumen  yields  on  ignition: 

24.0% 

19.5% 

1.2% 

.8% 

268 


THE   MODERN   ASPHALT  PAVEMENT. 


character  than  those  prepared  from  California  petroleum  and,  no 
doubt,  for  the  same  reason.  That  they  are  very  variable  in  char- 
acter can  be  seen  from  the  results  of  an  examination  of  five 
samples,  taken  from  one  delivery,  which  were  submitted  to  the 
author  for  examination. 

RESIDUAL  PITCH  FROM  BEAUMONT,  TEXAS,  PETROLEUM 
TAKEN  FROM  ONE  DELIVERY. 


72550 

72589 

72590 

72591 

72592 

Penetration  at  78°  F./780  F  

10° 

16° 

93° 

58° 

81° 

Flow  

None 

None 

100  0% 

76  0% 

86  0% 

98.1% 

97  7% 

99  3 

99  0 

99  1 

Difference  

1.8 

2.2 

.4 

.9 

5 

Inorganic  or  mineral  matter. 

1 

1 

3 

1 

4 

Carbenes: 
Bitumen    insoluble    in    carbon 
tetrachloride,air  temperature. 

Bitumen  yields  on  ignition: 
Fixed  carbon  

100.0 
10.5% 

100.0 

12.7% 
23.0% 

100.0 
6.7% 

100.0 
7.0% 

100.0 
6-7% 

In  this  delivery  material  was  found  which  was  so  hard  as  to 
hardly  flow  at  212°  F.  (No.  72550)  and  so  soft  as  to  be  readily 
melted  (No.  72590). 

Other  lots  which  have  been  examined  by  the  author  have 
shown  an  equal  lack  of  uniformity,  as  can  be  seen  from  the  follow- 
ing figures: 

RESIDUAL  PITCH  FROM  BEAUMONT,  TEXAS,  PETROLEUM. 


Test  number  

63526 

63527 

63528 

Penetration  at  78°  F./780  F  

Too  soft 

110° 

15° 

98.3% 

96.6%. 

95.7% 

Malthenes  : 
Bitumen  soluble  in  88°  naphtha,  air  tempera- 
ture   

78.2% 

72.2% 

67.9% 

This  is  per  cent  of  total  bitumen  

79.6 

74  7 

71  0 

Carbenes  : 
Bitumen   insoluble   in    carbon  tetrachloride, 

8  6% 

12.8% 

12  5% 

Bitumen  yields  on  ignition: 
Fixed  carbon.  . 

14.5% 

17.6% 

21.1% 

RESIDUAL  PITCHES. 


269 


The  most  important  characteristic  of  the  residual  pitches  from 
Texas  oil  is  that  they  yield,  as  prepared,  and  as  found  on  the 
market,  more  than  20  per  cent  of  fixed  carbon  as  compared  with 
15  per  cent  for  the  California  pitches.  This  characteristic  while 
it  may  be  due  somewhat  to  the  fact  that  the  Texas  pitch  is  a  denser 
material,  because  the  distillation  has  been  carried  to  a  point  beyond 
that  to  which  the  California  oil  is  submitted,  is  an  important  one 
industrially  as  it  makes  it  possible  to  differentiate  and  determine 
the  origin  of  any  of  these  forms  of  bitumen.  The  two  can  also  be 
differentiated  by  determining  whether  paraffine  is  present,  none 
being  found  in  the  California  products  and  about  1  per  cent  in 
those  from  Texas. 

Examples  of  the  variation  in  the  character  of  Texas  residual 
pitches  as  revealed  by  the  percentage  of  carbenes  which  they  con- 
tain is  shown  by  the  folio  whig  analyses: 

RESIDUAL    PITCHES   FROM    BEAUMONT,   TEXAS,  PETROLEUM. 


Bitumen  Insolu- 

Test Number. 

ble  in  Carbon 
Tetrachloride, 

Air  Temperature. 

63526 

8.6% 

63527 

12.8 

63528 

12.5 

68943 

5.1 

69015 

5.1 

72550 

10.5 

72589 

12.7 

72590 

6.7 

72591 

7.0 

72592 

6.7 

The  amount  is  generally  much  larger  than  is  found  in  the  more 
carefully  prepared  California  "  D  "  grade  asphalt  and  points  to 
overheating  in  the  preparation  of  these  particular  specimens. 
This  is  much  greater  in  the  pitch  which  has  been  produced  in  1907 
than  in  the  supply  of  1903.  The  material  has  recently  been  of 
very  poor  quality,  and,  in  the  opinion  of  the  author,  it  is  entirely 
unsuitable  for  use  in  the  paving  industry. 


270 


THE  MODERN  ASPHALT  PAVEMENT. 


Ebano  Asphalt. — A  residual  pitch  made  from  the  asphaltic 
oil  or  maltha  occurring  at  Ebano,  Mexico,  about  thirty  miles 
from  Tampico,  on  the  line  of  the  Mexican  Central  Railroad,  has 
been  on  the  market  in  the  United  States  and  abroad,  for  a  few 
years,  under  the  designation  of  "Ebano  Asphalt,  "a  well  sunk 
at  that  point  to  a  depth  of  1600  feet,  producing  from  1200  to 
1500  barrels  of  petroleum  a  day.  It  corresponds  in  its  preparation 
and  characteristics  to  the  California  residual  pitches.  Following 
are  the  results  of  examinations  of  various  grades  of  the  material: 


T1  6st  number                                       •  •  . 

102261 

102262 

102263 

102264 

"E" 

"DX" 

"D" 

"B" 

PHYSICAL  PROPERTIES. 

Penetration  at  78°  F.  —  Bowen  

62 

30 

26 

7 

Softens  

125°  F. 

185°  F. 

190°  F. 

260°  F. 

163°  F. 

200°  F. 

206°  F. 

278°  F. 

CHEMICAL  CHARACTERISTICS. 

Bitumen  soluble  in  CS2,  air  temp  

99.4% 

97.9% 
2 

97.8% 
none 

95.8% 
3 

.5 

1.9 

2  2 

3  9 

Carbenes: 
Bitumen  insoluble  in  carbon  tetra- 
chloride,  air  temperature  

100.0% 

.4% 

100.0% 
14.4% 

100.0% 
15.5% 

100.0% 
19.7% 

Malthenes: 
Bitumen  soluble  in  88°  naphtha,  air 
temperature  

69.0% 

66.0% 

55  5% 

48  1% 

This  is  per  cent  of  total  bitumen  .... 
Per  cent  of  soluble  bitumen  removed 
byH2SO4  

69.4 
89.0 

66.5 
91.0 

56.3 
92.0 

50.2 
93.0 

Bitumen  yields  on  ignition: 
Fixed  carbon  

19.2% 

23.9% 

24  9% 

30  5% 

Paraffine  scale  

1.0% 

1.3% 

1.3% 

1.9% 

Where  the  Ebano  asphalt  is  made  of  "  E  "  grade  consistency, 
it  seems  to  be  of  a  character  as  good  as  that  of  the  same  material 
made  in  California,  but  where  the  distillation  has  been  carried  to 
such  a  point  that  the  consistency  is  much  harder,  the  percentage 
of  carbenes  present  shows  that  the  bitumen  has  been,  at  least 
in  some  cases,  very  seriously  decomposed  and  such  a  product 
is,  on  this  account,  very  unsatisfactory. 

Baku  Pitch. — On  the  Continent  a  residual  pitch  from  the 
distillation  of  Russian  petroleum  is  an  industrial  product.  This 
hae  the  following  composition: 


RESIDUAL   PITCHES.  271 

BAKU  PITCH. 
Test  number 63200 

PHYSICAL    PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original  substance,  dry 1 . 1098 

Color  of  powder  or  streak Black 

Lustre Lustrous 

Structure Uniform 

Fracture Semi- 

conchoidal 

Hardness,  original  substance —  1 

Odor Petroleum 

Softens 140°  F. 

Flows 150°  F. 

Penetration  at  78°  F 10° 

CHEMICAL  CHARACTERISTICS. 

Bitumen  soluble  in  CS2,  air  temperature 91 . 6% 

Difference 8.4 

Inorganic  or  mineral  matter Trace 

100.0 
Malthenes: 

Bitumen  soluble  in  88°  naptha,  air  temperature 54.6% 

This  is  per  cent  of  total  bitumen 59 . 6 

Per  cent  of  soluble  bitumen  removed  by  H^C^ 44 . 1 

Per  cent  of  total  bitumen  as  saturated  hydrocarbons 33 .3 

Bitumen  soluble  in  62°  naphtha 61 . 3% 

This  is  per  cent  of  total  bitumen 66 . 9 

Carbenes: 

Bitumen  insoluble  in  carbon  tetrachloride,  air  temp 10 . 4% 

Bitumen  yields  on  ignition: 

Fixed  carbon 26.8% 

Paraffine  scale 1 . 7% 

This  pitch  has  a  comparatively  high  density,  yields  a  large  per- 
centage of  fixed  carbon,  bitumen  insoluble  in  cold  carbon  tetra- 
chloride and  much  organic  matter  not  bitumen;  showing  that  the 
distillation  has  been  pushed  to  an  extreme.  It  contains  1.7  percent 
of  paraffine  scale.  It  is  a  remarkable  fact  that  the  softening-point 
of  this  material  is  much  nearer  that  of  the  California  residue  than  of 


272  THE  MODERN  ASPHALT  PAVEMENT. 

that  from  Beaumont,  Texas,  oil.  It  might,  perhaps,  be  possible 
to  use  a  small  amount  of  this  bitumen  in  the  paving  industry  as 
an  amendment  to  some  asphalts. 

Solid  Bitumens  the  Product  of  the  Condensation  of  Heavy 
Oils.  —  Another  class  of  bitumens  are  the  artificial  ones  obtained 
by  the  treatment  of  any  of  the  fluxes  which  have  been  described 
with  sulphur  or  oxygen  at  high  temperatures.  In  then-  uses  and 
consistency  they  may  be  ranked  between  the  fluxes  and  the  solid 
bitumens. 

Pittsburg  Flux.  —  The  first  bitumen  of  this  description  to  be 
put  upon  the  market  was  known  as  Pittsburg  Flux.  It  was  made 
by  adding  to  an  ordinary  Pennsylvania  petroleum  residuum  about 
one  pound  of  sulphur  to  every  gallon  of  oil  and  heating  the 
material  to  a  point  a  little  below  that  of  distillation  and  main- 
taming  it  at  that  temperature  until  the  evolution  of  hydrogen 
sulphide  ceases.  The  residuum  is,  in  this  way  converted  into  a 
semi-solid  cheesy  bitumen  which  is  very  short,  that  is  to  say, 
has  little  ductility,  and  is  very  slightly  susceptible  to  changes  of 
temperature.  The  reaction  which  takes  place  is  represented  by 
the  following  equation: 


The  reaction,  in  reality,  is  not  as  simple  as  this  but  the  result  is 
explained  as  well.  Two  molecules  are  condensed  to  one  with 
the  accompanying  evolution  of  hydrogen  sulphide  gas  and  with 
the  resulting  changes  in  the  properties  of  the  bitumen.  The  great 
expense  incurred  for  sulphur  in  this  process  made  it  necessary  to 
utilize  the  by-product  of  hydrogen  sulphide.  This  was  done  by 
converting  it  into  sulphuric  acid.  The  business  was  not  profitable 
even  under  these  conditions  and  was  soon  abandoned.  The  mate- 
rial could  not  be  used  as  the  principal  source  of  bitumen  in  making 
an  asphalt  cement,  being  too  short,  and  only  as  an  addition,  in 
small  amounts,  to  the  ordinary  asphalts.  Used  hi  this  way  it 
has  been  successful  in  one  or  two  instances. 

An  analysis  of  this  material  is  presented  in  the  table  on  page  275. 

Ventura  Flux.  —  Later  on  an  attempt  was  made  to  make  a 
similar  substance  from  the  asphaltic  petroleum  of  California.  The 


RESIDUAL  PITCHES.  273 

product  was  a  slight  improvement  on  the  Pittsburg  Flux  but  pave- 
ments made  with  it  without  the  addition  of  native  solid  bitumen 
were  failures  in  Allegheny,  Pa.  Its  manufacture  was  abandoned 
after  a  few  years. 

Byerlyte. — In  the  meantime  Byerly,  of  Cleveland,  had  found 
that  the  oxygen  of  the  air  was  as  satisfactory  a  condensing  agent 
as  sulphur,  imitating  the  practice  of  blowing  certain  vegetable 
and  fish  oils  in  order  to  thicken  them  and  give  them  greater  viscosity. 
He  produced  a  substance  similar  to  Pittsburg  Flux  by  drawing 
air  through  residuum  while  the  latter  was  maintained  at  a  high 
temperature.  Depending  on  the  length  of  time  during  which 
the  air  was  allowed  to  act  the  product  was  soft  or  as  hard  as  pitch. 
This  material  has  been  used  to  some  extent  in  making  asphalt 
blocks  in  Washington,  but  even  this  use  has  now  been  abandoned. 
In  mixture  in  small  proportion  with  the  native  solid  bitumens 
it  can  be  used  but  there  is  no  advantage  in  doing  so  commen- 
surate with  the  expense  involved  in  the  treatment  of  the  original 
residuum. 

Hydroline  "  B." — Still  more  recently  the  asphaltic  residuum 
from  the  asphaltic  petroleums  of  Texas  has  been  put  upon  the  mar- 
ket, after  having  been  blown,  under  the  name  Hydroline-  "  B." 
It  possesses  in  this  form  no  qualities  which  could  recommend  it 
very  strongly  for  paving  purposes  except,  perhaps,  as  an  amend- 
ment to  certain  inferior  asphalts  and  it  need  hardly  be  considered 
here. 

Sarco  Asphalt. — This  material,  which  has  recently  been  on 
the  market,  is  a  blown  product  like  Hydroline  '  *B,"  prepared 
from  Kansas  residuum,  and  it  possesses  much  the  same  properties, 
having  little  ductility  and  being  very  short. 

A  specimen  recently  examined  in  the  author's  laboratory, 
showed  the  following  characteristics: 

Test  number 96891 

PHYSICAL  PROPERTIES. 

Specific  gravity,  78°  F./780  F.,  original  substance,  dry 981 

Softens 190°  F. 

Flows 210°  F. 

Penetration  at  78°  F.— Bowen 120° 

Condition  at  140°  F.  after  1  hour { 


274  THE  MODERN  ASPHALT  PAVEMENT. 

CHEMICAL  CHARACTERISTICS. 

Bitumen  soluble  in  CS2,  air  temperature 99 . 1% 

Inorganic  or  mineral  matter .7 

Difference .2 

100.0% 
Malthenes: 

Bitumen  soluble  in  88°  naphtha,  air  temperature 69 .8% 

This  is  per  cent  of  total  bitumen 70 . 4 

Carbenes: 

Bitumen  insoluble  in  carbon  tetrachloride,  air  temperature .  2% 

Bitumen  yields  on  ignition: 

Fixed  carbon , 10 .3% 

Paraffine  scale 12 .3% 

It  is  notable  for  the  very  high  percentage  of  paraffine  scale 
which  it  contains,  which,  in  addition  to  the  properties  conferred 
by  blowing  the  oil  with  air,  adds  to  its  shortness.  It  is  made 
of  several  grades,  having  a  penetration  of  from  50  to  that  of  the 
sample  which  was  examined. 

According  to  analyses  made  by  Mr.  Francis  P.  Smith,  three 
specimens  which  he  examined  had  the  following  properties: 

Test  number 1175  1176  1210 

Melting-point,  degrees  F 171  188  198 

Penetration  at  32°  F.(Dow,  1  rain.,  200  gms.) ...  42  49  31 

Penetration  at  77°  F.  (Dow,  5  sec.,  100  gms.) ...  60  70  45 

Penetration  at  115°  F.  (Dow,  5  sec.,  50  gms.)  .  .  97  85  71 

Bitumen  soluble  in  CS, . 98.0%  97.7%  98.7% 

Organic  insoluble 1.0  1.8  1.3 

Ash 1.0  .5  Trace 

Naphtha  soluble  bitumen 79 .9%  79 .0%  79 . 2% 

Naphtha  soluble  bitumen  (per  cent  total  bit.)  ..81.5  80 . 9  80 . 3 

Loss  on  heating  5  hours  at  325°  F 08%  .4%  .  15% 

Penetration  after  heating 60  61  33 

Ductility 3  cm.  3  cm.  2  cm. 

Fixed  carbon 10.6%  10.8%  10.8% 

It  is  hardly  possible  that  a  satisfactory  pavement  could  be 
made  with  such  material,  although  it  might  be  combined  to  a 
certain  extent  with  the  ordinary  asphalts. 

The  character  of  Pittsburg  Flux;  Byerlyte  and  Hydroline  "  B  " 
is  shown  in  the  table  on  page  275. 

From  these  figures  it  appears  that  the  materials  are  nearly 
pure  bitumens  and  that,  not  having  been  subjected  to  suffi- 
ciently high  temperatures  to  produce  cracking,  the  amount  of 
bitumen  insoluble  in  carbon  tetrachloride  is  practically  nothing. 
According  to  their  derivation  the  materials  carry  more  or  less 
paraffine  but  the  Hydroline  "  B  "  being  derived  from  a  Texas  oil 


RESIDUAL  PITCHES. 


275 


6123 

Byerlyte 

(paving) 

1.023 
Black 
Dull 
Uniform 
Cheesy 
Petroleum 
245°  F. 
294°  F. 
63° 

.93% 
Smooth 

5-9% 
Smooth 

99.7% 
.3 
.0 

100.0 

62.0% 
62.2 

25.5 
46.3 

67.2% 
67.4 

•  4% 

18.0% 
4.6% 

6124 

Byerlyte 

(roofing) 

.9070 
Black 
Dull 
Uniform 
Cheesy 
Petroleum 
230°  F. 
254°  F. 
107° 

1-8% 
Smooth 

6.5% 
Smooth 

i 

99.£>% 
.5 
.0 

71436 

Hydro- 
line  "B". 

1.0043 
Black 
Dull 
Uniform 
Cheesy 
Petroleum 
206°  F. 
220°  JF. 
55° 

1.0% 

Smooth 
penetra- 
tion, 45° 

5.8% 
Smooth 
penetra- 
tion, 40° 

99.9% 
.1 
.0 

Pittsburg 
Flux 

.9879 
Black 
Dull 
Uniform 
Cheesy 
Petroleum 
295°  F. 
353°  F. 
74° 

1.7% 
Smooth 

4.4% 
Blistered 

99.7% 
.3 
.0 

PHYSICAL   PROPERTIES. 

Specific  gravity,   78°  F./780  F., 
original  substance,  dry  

Color  of  powder  or  streak  

Lustre   • 

Structure                                     .  . 

Fracture                      

Odor             

Softens         

Flows       

Penetration  at  78°  F 

CHEMICAL   CHARACTERISTICS. 

Dry  substance  : 
Loss  325°  F    7  hours 

Character  of  residue  . 

Loss,   400°  F.,  7   hours    (fresh 
sample)   

Character  of  residue  

Bitumen  soluble  hi  CS*  air  temp. 
Difference  .  .                         

Inorganic  or  mineral  matter 

Malthenes  : 
Bitumen  soluble  in  88°  naphtha, 
air  temperature  

100.0 

67.1% 
67.3 

14.8 
57.3 

71.5% 
71.7 

.3% 

14.7% 
10.3% 

100.0 

66.8% 
67.1 

17.4 
55.5 

72.0% 
72.3 

•  3% 

14.3% 

5.7% 

100.0 

69.3% 
69.4 

12.7 
60.6 

.5% 

12.2% 
1-0% 

This  is  per  cent  of  total  bitumen. 
Per  cent  of  soluble  bitumen  re- 
moved by  H2SO4  
Per  cent  of  total  bitumen  as  sat- 
urated hydrocarbons  

Bitumen  soluble  in  62°  naphtha 
This  is  per  cent  of  total  bitumen. 

Carbenes  : 
Bitumen  insoluble  in  carbon  te- 
trachloride,  air  temperature.  . 

Bitumen  yields  on  ignition  : 
Fixed  carbon 

Paraffine  scale  

276  THE  MODERN  ASPHALT  PAVEMENT. 

contains  no  more  than  is  found  in  the  residual  pitch  from 
the  same  oil.  It  is  worthy  of  remark  as  to  Byerlyte  that, 
although  made  from  paraffine  oil,  it  contains  much  less  paraf- 
fine  scale  than  would  be  expected,  and  would  point  to  the  fact 
that  this  material  has  become  altered  in  the  process  of  manu- 
facture. 

With  none  of  these  materials,  as  the  principal  constituent  of 
a  paving  cement,  is  it  possible  to  produce  a  satisfactory  surface 
mixture.  They  are  all  too  short,  but  they  may  be  used  as  an 
amendment  in  an  amount  not  exceeding  10  per  cent.  Owing  to 
the  fact  of  their  great  lack  of  susceptibility  to  change  in  con- 
sistency within  wide  ranges  of  temperature  they  present  some 
advantages. 

Differentiation  of  the  Residual  Pitches  from  the  Natural 
Asphalts. — The  residual  pitches,  it  appears  from  the  preceding 
data,  contain  practically  no  mineral  matter.  With  only  one  excep- 
tion there  is  no  native  bitumen  in  use  in  the  asphalt  paving  indus- 
try which  has  the  same  characteristic.  It  is,  therefore,  possible 
to  differentiate,  except  in  the  case  of  gilsonite,  an  oil  asphalt, 
so-called,  from  a  native  bitumen  by  determining  the  amount  of 
mineral  matter  present.  The  mineral  matter  in  the  latter  is 
generally  of  a  ferruginous  nature  while  that  derived  from  the 
native  bitumens  generally  contains  silica.  A  microscopic  exam- 
ination of  the  residue  left  on  ignition  will,  therefore,  aid  in  the 
determination.  Even  in  the  case  of  gilsonite  the  color  of  the 
ash  is  quite  different  from  that  obtained  from  the  residual  pitches. 
Unfortunately  the  amount  of  fixed  carbon  which  the  California 
"  D  "  grade  asphalt  yields  and  that  from  the  native  bitumens 
is  so  nearly  the  same  that  this  characteristic  cannot  be  success- 
fully used,  although  the  amount  obtained  may  be  of  value  as 
indicating  the  presence  of  grahamite  which  in  itself  has  a  high 
fixed  carbon.  The  native  bitumens  carry,  however,  less  bitu- 
men insoluble  in  cold  carbon  tetrachloride  but  soluble  in  carbon 
disulphide  than  the  residual  pitches,  unless  the  latter  are  very 
carefully  made,  and  in  case  of  doubt  the  differentiations  of  the 
two  classes  of  materials  may  be  assisted  by  comparative  deter- 
minations of  this  form  of  bitumen. 

SUMMARY. 

All  petroleums  on  evaporation  under  suitable  conditions  leave 
a  pitchy  residue.  The  residue  from  the  asphaltic  or  semi-asphaltic 


RESIDUAL  PITCHES.  277 

petroleums  resembles  the  native  asphalts.  The  principal  supplies 
available  for  use  in  the  paving  industry  are  residual  pitches  from 
California  and  from  Texas  oil.  These  are  each  made  in  such  a 
careless  way  that  they  consist  largely  of  alteration  products  of 
the  original  hydrocarbons  as  shown  by  the  lack  of  solubility  of 
some  of  their  constituents  as  compared  with  those  found  in  the 
original  oil.  On  this  account  the  material  is  not  always  satisfac- 
tory and,  moreover,  requires  great  skill  to  use  it. 

The  residual  pitches  from  Texas  and  from  California  oils  can 
be  readily  differentiated  by  certain  characteristics,  that  from  the 
Texas  oil  generally  yielding  a  higher  percentage  of  fixed  carbon 
than  the  pitch  obtained  from  the  California  oil. 

The  blown  or  oxidized  petroleum  residues  are  characterized 
by  their  lack  of  susceptibility  to  temperature  changes,  but  are 
extremely  short,  which  prevents  their  use  as  the  main  source  of 
bitumen  in  the  paving  mixture.  Pavements  laid  with  them  have 
generally  eventually  proved  failures.  They  may  possess  some 
desirable  qualities  as  an  amendment  to  the  native  asphalt  to 
an  extent  not  exceeding  10  per  cent,  and,  used  in  this  way,  should 
be  considered  as  fluxes. 


CHAPTER  XIV. 

COMPARISON  OF  VARIOUS  NATIVE  ASPHALTS  AND  THEIR 
RELATIVE  MERITS  FOR  PAVING  PURPOSES. 

In  attempting  to  form  an  opinion  on  the  availability  of  any 
native  bitumen  for  paving  purposes  a  number  of  things  must  be 
taken  into  consideration,  which  may  be  tabulated  as  follows: 

1.  The  quantity  available. 

2.  Its  uniformity  in  character. 

3.  Its  stability  in  a  melted  condition  at  high  temperatures. 

4.  Its  stability  in  consistency  at  the  extremes  of  temperature 
which  it  meets  in  an  asphalt  pavement. 

5.  The  proportion  of  malthenes  to  asphaltenes  which  it  con- 
tains. 

6.  The  proportion  of  flux  which  is  required  to  make  an  asphalt 
cement. 

7.  Mineral  matter  present  and  its  character. 

i.  The  Quantity  Available. — No  native  bitumen  can  be  of  any 
great  importance  in  the  paving  industry  without  a  large  supply 
of  ^t  is  available.  Pavements  can  no  doubt  be  constructed  of  a 
bitumen  of  which  not  more  than  500  to  1000  tons  can  be  gathered 
together  with  difficulty  in  any  one  year,  but  such  supplies  are  too 
unreliable  to  permit  of  their  being  of  permanent  interest.  There 
are  hundreds  of  such  deposits  in  which  many  thousands  of  dollars 
have  been  sunk  without  any  adequate  return  for  the  investment. 
A  deposit  to  be  of  any  great  value  should  afford  a  supply  of  at 
least  50,000  tons  annually  without  difficulty.  The  first  thing 
to  be  done,  therefore,  in  considering  the  availability  of  native  bitu- 
men is  to  learn  whether  the  deposit  is  such  that  the  amount  which 

278 


COMPARISON  OF  VARIOUS  NATIVE  ASPHALTS.  279 

can  be  obtained  from  it  will  prove  large  enough  to  be  of  industrial 
importance. 

2.  Its  Uniformity  in  Character. — A  great  consideration  in  the 
turning  out  of  a  regular  asphalt  surface  mixture  is  that  the  bitu- 
men from  which  it  is  made  shall  be  of  such  a  nature  that  every 
cargo  or  shipment  of  it  may  be  exactly  like  all  others.     If  this 
is  not  the  case  each  lot  will,  of  necessity,  require  a  different  method 
of  handling,  which  necessitates  great  experience  and  skill  which 
are  not  always  to  be  found  among  those  who  are  engaged  in  the 
laying  of  asphalt  pavements. 

3.  Its  Stability  in  a  Melted  Condition  at  High  Temperatures. — 
As  the  asphalt  cement  made  from  the  native  bitumens  as  they 
occur  in  the  refined  condition  in  the  trade  is  necessarily  main- 
tained in  a  melted  condition  at  high  temperature  for  considerable 
periods  of  time  it  is  equally  important  that  it  should  consist  of  a 
bitumen  which  does  not  become  changed  in  consistency,  under 
these  conditions,  owing  to  the  rapid  volatilization  of  certain  of 
its  constituents. 

There  is  a  very  decided  difference  in  the  behavior  of  different 
bitumens  in  this  respect  and  this  should  be  borne  in  mind  in  deter- 
mining whether  one  has  a  preference  over  another  for  use  in  the 
construction  of  asphalt  pavements. 

4.  Its  Stability  in  Consistency  at  the  Extremes  of  Tempera- 
ture which  it  Meets  hi  an  Asphalt  Pavement. — There  is  a  difference 
in  the  behavior  of  different  bitumens,  as  far  as  their  consistency 
is  concerned,  at  the  extremes  of  temperature  which  are  met  with 
in  summer  and  winter,  that  is  to  say,  some  of  them  are  much 
more  susceptible  to  changes  in  consistency  between  very  low  and 
very  high  temperatures  than  others.     This  is  an  important  con- 
sideration since,  although  a  given  bitumen  may  enable  one  to  con- 
struct an  asphalt  surface  which  is  of  proper  consistency  at  medium 
temperature,  say  78°  F.,  it  may  become  extremely  hard  and  brittle 
at  zero  or  extremely  soft  and  oily  at  120°  F.,  a  temperature  which 
asphalt  surfaces  frequently  reach  under  our  hot  summer  sun. 

5.  The  Proportion  of  Malthenes  to  Asphaltenes  which  it  Con- 
tains.— The  relative  proportion  of  malthenes,  those  constituents 
which  are  soluble  in  light  petroleum  naphtha,  and  of  asphaltenes, 


280  THE  MODERN  ASPHALT  PAVEMENT. 

the  other  constituents  not  soluble  in  this  medium,  has  a  bearing 
upon  the  availability  of  any  native  bitumen  for  paving  purposes. 
Although  to-day  the  deficiencies  in  this  respect  may  be  modified 
by  the  use  of  certain  fluxes,  which  supply  the  missing  constituents, 
this  is  not  always  the  case  and,  when  it  is  so,  it  requires  very 
considerable  skill  to  accomplish  it.  This  has  been  illustrated  more 
fully  in  another  place.1 

6.  The  Proportion  of  Flux  which  is  Required  to  Make  an 
Asphalt  Cement. — The  question  of  the  amount  of  flux  which  is 
necessary  to  use  with  any  bitumen  is  one  of  importance.     If  the 
native  bitumen  is  so  hard  as  to  require  a  very  large  percentage 
of  flux  there  is  a  very  great  probability,  although  this  is  not  uni- 
versally the  case,  that  the  resulting  cement  will  be  too  oily  and 
too  susceptible  to  high  temperature. 

Gilsonite  is  a  bitumen  which  is  an  exception  to  this  rule.  To 
flux  this  material  in  making  an  asphalt  cement,  about  equal  parts 
of  it  and  of  heavy  asphaltic  oil  are  necessary,  but  the  cement 
contains  normal  proportions  of  malthenes  soluble  in  88°  naphtha, 
and  of  asphaltenes  insoluble.  Such  a  cement  has  an  extremely 
rubbery  consistency  and  a  considerable  amount  of  elasticity, 
a  cylinder  of  the  cement  springing  back  to  its  original  formation 
when  bent  nearly  double.  Such  a  cement,  in  addition,  is  not  as 
susceptible  to  temperature  changes  as  those  made  from  the  ordi- 
nary asphalts.  A  statement  in  regard  to  the  relative  proportions 
of  various  fluxes  which  must  be  combined  with  the  various  asphalts 
to  produce  cements  of  different  penetrations  is  given  on  page  308. 

7.  Mineral  Matter  Present  and  its  Character. — The   mineral 
matter  present  in  any  native  bitumen  may  be  desirable  or  unde- 
sirable.    If  it  contains  so  much  or  if  it  is  so  coarse  as  to  render 
it  impossible  to  maintain  it  uniformly  in  suspension  in  the  melted 
asphalt  cement  which  is  prepared  from  the  bitumen  it  is  undesir- 
able.    If,  on  the  other  hand,  it  is  extremely  fine  and  acts  as  a 
filler,  as  in  the  case  of  Trinidad  asphalt,  it  is  very  desirable. 

The  fact  that  it  may  reduce  the  percentage  of  bitumen  present 
is  of  no  importance,  since  in  the  case  of  an  asphalt  consisting  of 

1  See  pages  139  and  178. 


COMPARISON   OF  VARIOUS  NATIVE  ASPHALTS.  281 

99  per  cent  of  bitumen  it  will  be  necessary  in  building  up  a  satis- 
factory surface  mixture  to  add  a  certain  amount  of  filler  which 
cannot  be  done  as  successfully  by  any  artificial  means  as  is  done 
by  nature. 

In  this  connection  the  following  correspondence  between  the 
President  of  the  Board  of  Public  Works  of  a  western  city  and  a 
local  chemist,  many  years  ago,  may  prove  of  interest  as  well  as 
the  latter's  answers  to  several  other  questions  which  are  frequently 
asked. 

"  May  22,  1893. 

"  DEAR  SIRS: — A  discussion  has  been  going  on  in  this  city, 
which  the  citizens  are  largely  interested  in,  in  regard  to  asphalt 
paving. 

"  It  is  claimed  on  one  hand  that  asphalt  is  asphalt,  no  matter 
where  it  is  found,  and  the  only  difference  in  asphalts  is  in  the 
amount  of  bitumen  which  they  contain.  As  a  well-known  and 
practical  chemist  in  this  city,  I  would  thank  you  to  answer  the 
following  questions,  and  send  me  a  bill  for  your  expert  opinion. 

"  1.  Does  the  percentage  of  bitumen  determine  the  value 
of  an  asphalt  for  paving  purposes? 

"2.  May  or  may  not  an  asphalt  contain  a  very  large  percent- 
age of  bitumen  and  still  be  worthless  for  paving  purposes? 

"  3.  Might  or  might  not  an  asphalt,  which  in  its  natural  state 
is  good  for  paving  purposes,  be  so  destroyed  by  heat  that  it  is 
practically  worthless  for  paving  purposes,  and  still  the  material 
after  subjection  to  heat,  be  asphalt? 

"  4.  Might  or  might  not  two  asphalts  contain  the  same  amount 
of  bitumen,  and  one  be  so  unstable  that  it  will  not  stand  expo- 
sure to  the  sun,  and  the  other  be  comparatively  permanent? 

"  5.  Is  it  possible  that  one  asphalt  might  contain  twice  as 
much  bitumen  as  another,  and  still  be  far  inferior  for  street  con- 
struction to  the  one  containing  a  less  quantity? 

"  6.  Is  there  any  real  system  by  which  a  chemist  can  tell  to  a 
certainty,  by  analysis,  whether  a  given  asphalt  which  has  never 
been  tried  will  make  as  good,  permanent,  and  durable  a  pave- 
ment as  another  which  has  proved  a  success? 

"  7.  Are  there  or  are  there  not  qualities  required  of  an  asphalt 


282  THE  MODERN  ASPHALT  PAVEMENT. 

for  paving  purposes  which  makes  it  impossible  for  a  chemist  who 
has  not  made  the  subject  a  special  study,  to  state  for  a  certainty 
whether  a  given  untried  asphalt  will  make  as  good  a  pavement 
as  another  asphalt  which  has  proved  a  success? 

"  8.  What  is  the  real  test  of  standard  or  quality  which  will 
give  the  value  of  an  asphalt  for  paving  purposes? 

"9.  Might  an  asphalt  pavement  stand  for  one  or  two  years, 
and  fail  from  effect  of  elements  in  succeeding  years,  and  might 
two  asphalts  stand  equally  for  two  years  and  show  marked  differ- 
ences in  wear  in  succeeding  years? 

"  An  early  reply  will  oblige, 

"Yours  respectfully, 

(Signed)  "PRESIDENT  BOARD  OF  PUBLIC  WORKS.'! 

In  reply  to  the  above  questions  the  following  opinion  was 
rendered : 

"1st  Answer.  The  percentage  of  bitumen  does  not  determine 
the  value  of  an  asphalt  for  paving  purposes. 

"  2d  Answer.  An  asphalt  might  contain  a  very  large  percentage 
of  bitumen,  and  still  be  comparatively  worthless  for  paving  pur- 
poses. 

"  3d  Answer.  An  originally  good  asphalt  for  paving  purposes 
might  be  so  altered  by  heat  as  to  be  practically  worthless,  and  yet 
the  altered  material  would  still  be  asphalt  in  the  sense  that  it  could 
not  be  distinguished  from  asphalt,  notwithstanding  its  marked 
inferiority  to  the  particular  asphalt  from  which  it  was  produced. 

"  4th  Answer.  Two  asphalts  might  contain  the  same  amounts 
of  bitumen  and  yet  possess  entirely  different  powers  of  resistance 
to  the  destructive  action  of  the  elements.  One  might  thus 
be  comparatively  permanent  and  stable,  and  the  other  greatly  in- 
ferior. 

"  5th  Answer.  As  the  percentage  of  bitumen  in  an  asphalt 
does  not  determine  its  value  for  paving  purposes,  it  is  quite  pos- 
sible for  one  asphalt  to  contain  a  much  higher  percentage  than 
another  and  yet  be  decidedly  inferior  for  making  a  durable  pave- 
ment. 

"  6th  Answer.  There  is  no  system  of  chemical  analysis  that  will 


COMPARISON  OF  VARIOUS  NATIVE  ASPHALTS.  283 

determine  for  a  certainty  that  a  given  untried  sample  of  asphalt 
will  make,  in  every  way,  as  good  a  pavement  as  another  asphalt 
which  has  proved  a  success. 

"7th  Answer.  The  requirements  of  an  asphalt  for  paving 
purposes  are  of  such  a  peculiar  nature  that  it  would  be  impossible 
for  a  chemist  who  had  not  made  the  subject  a  special  study  to 
state  with  certainty,  from  the  results  of  analysis,  whether  or  not  a 
given  sample  would  make  as  good  a  pavement  as  an  asphalt  which 
has  proved  a  success. 

"  8th  Answer.  The  real  and  final  test  of  the  quality  of  an 
asphalt  for  paving  purposes  is  actual  trial  for  a  proper  length  of 
time.  Proper  chemical  and  physical  tests  of  a  new  variety  of 
asphalt  may  strongly  indicate  its  probable  value  as  a  paving  mate- 
rial, but  these  tests,  though  of  great  assistance  in  forming  an 
opinion,  really  only  show  the  advisability  of  submitting  the  asphalt 
to  the  final  and  infallible  test  of  actual  trial. 

"  9th  Answer.  A  test  of  one  or  two  years  under  any  condition 
demonstrates  only  that  that  particular  asphalt  pavement  is  good 
for  that  length  of  time  under  those  conditions,  and  does  not  demon- 
strate how  much  longer  it  will  last  under  the  same  conditions  or 
whether  it  will  last  as  long  under  other  or  more  unfavorable  con- 
ditions. Two  asphalt  pavements  might  endure  equally  well  for 
a  given  short  time,  and  yet  show  decided  difference  under  a  long 
trial. 

"Having  thus  briefly  answered  the  questions  asked  it  may, 
perhaps,  be  well  to  give  some  explanation  of  the  subject,  in  order 
to  indicate  the  reasons  for  the  opinions  expressed.  First  of  all, 
it  may  be  stated  that  asphalt  is  not  a  chemical  compound  or  mineral 
of  fixed  and  invariable  composition.  According  to  Dana  it  is  a 
mixture  of  hydrocarbons,  and  the  asphalts  of  different  localities 
have  various  compositions.  Mineralogically,  bitumen  is  simply 
another  name  for  asphalt  or  asphaltum.  In  paving  parlance, 
however,  bitumen  has  come  to  mean  only  the  pure  portion,  so  to 
speak,  of  the  asphalt,  the  latter  term  being  applied  to  the  entire 
mixture  of  earthy  and  other  impurities  with  the  true  bitumen. 
This  view  of  bitumen  having  evidently  been  taken  in  the  ques- 
tions asked,  it  was  similarly  considered  in  the  replies.  It  is  to 


284  THE  MODERN  ASPHALT  PAVEMENt. 

be  understood,  then,  that  asphalt  is  an  impure  bitumen,  and  that 
bitumen  is  the  pure  article  considered  by  Dana  in  his  Mineralogy. 
But,  as  before  stated,  bitumen  has  no  fixed  composition  or  com- 
bination of  qualities.  Its  nature  and  physical  properties  are  as 
various  as  the  localities  where  it  is  found.  It  can  be  no  more 
strictly  defined  than  coal.  It  is  simply  a  mixture  of  various  hydro- 
carbons, and  may  be  either  a  solid  or  a  liquid.  Two  bitumens  of 
precisely  similar  percentage  composition  may  have  widely  different 
properties,  so  that  while  one  would  furnish  a  most  excellent  paving 
material  the  other  would  be  practically  worthless.  Such  instances 
of  substances  of  entirely  dissimilar  nature  having  the  same  per- 
centage composition  abound  in  chemistry.  Charcoal,  the  diamond, 
and  plumbago,  or  black  lead,  may  be  mentioned  as  a  familiar 
example.  Light  naphtha  or  gasoline  and  solid  paraffine  is  another. 
It  takes  more  than  an  ordinary  chemical  analysis  to  distinguish 
between  such  substances.  Evidently,  then,  the  mere  percentage 
of  bitumen  in  an  asphalt  would  not  determine  its  value  for  paving 
purposes,  for  this  bitumen  might  have  a  consistency  varying  any- 
where from  a  non-cohesive  liquid  to  a  brittle  worthless  solid.  By 
the  action  of  the  elements  all  asphalts  undergo  change.  This 
change  is  due  to  oxidation,  volatilization  and  other  molecular 
disruption,  and  tends  to  produce  greater  solidification  or  apparent 
drying,  and  the  asphalt  may  pass  through  all  the  stages  of  brittle- 
ness  to  final  crumbling  or  disintegration.  In  all  these  stages  the 
substance  is  still  asphalt,  although  at  many  points  it  is  evidently 
worthless  as  a  paving  material.  While  these  changes  are  slow 
in  nature,  some  of  them  may  be  greatly  hastened  by  the  applica- 
tion of  heat,  as  in  incautious  or  unskilful  refining  so  as  to  greatly 
injure  an  originally  good  asphalt.  It  is  evident,  also,  that  an 
asphalt  may  be  so  far  gone  in  the  process  of  natural  decay  that, 
while  it  may  serve  to  make  what  appears  to  be  an  excellent  pave- 
ment, the  life  of  such  a  pavement  must  be  comparatively  short. 
"  Having  thus  shown  how  much  depends  upon  the  quality  or 
nature  of  the  bitumen  in  an  asphalt  rather  than  upon  its  mere 
percentage,  it  becomes  important  to  know  to  what  extent  the 
chemist  can  distinguish  this  valuable  quality,  and  so  prevent  dis- 
astrous mistakes  in  pavement  work.  It  may  be  answered  that  a 


COMPARISON  OF   VARIOUS  NATIVE  ASPHALTS.  285 

chemist  who  has  made  a  special  study  of  the  subject  can,  by  proper 
chemical  analysis,  aided  by  certain  physical  tests,  point  out  what  is 
probably  good  or  worth  trying  in  the  case  of  new  varieties,  but  it 
is  impossible  for  him  to  state  for  a  .certainty  that  a  particular  new 
variety  will  be  fully  equal  in  every  essential  respect  to  some  stand- 
ard asphalt  that  has  proved  a  success.  Having  learned  by  experi- 
ence the  chemical  and  physical  differences  between  good  and  bad 
samples  of  any  particular  asphalt,  the  chemist  may  thereafter 
afford  valuable  assistance  in  the  use  of  that  asphalt. 

"  In  view  of  the  foregoing  facts  it  would  seem  that  the  extensive 
use,  for  paving  purposes,  of  any  variety  of  asphalt  that  has  not 
previously  been  proven  a  success  by  the  test  of  actual  trial  for  a 
sufficient  length  of  time,  under  sufficiently  adverse  conditions,  is 
in  the  nature  of  a  rather  hazardous  experiment. 

"  Trusting  that  the  above  answers  and  explanations  will  prove 
clear  and  satisfactory,  we  will  add  that  they  are  given  without 
prejudice  and  according  to  our  best  knowledge  of  the  subject, 

"  Yours  respectfully, 
(Signed)  "  CHEMIST." 

Action  of  Water  on  Asphalt  in  the  Laboratory. — It  has  fre- 
quently been  claimed  that  there  is  a  preference  for  one  asphalt 
over  another  based  upon  the  manner  in  which  it  behaves  towards 
water  when  it  is  placed  in  contact  with  it  in  the  laboratory.  From 
data  which  will  be  given  elsewhere  l  it  appears  that  this  method 
of  examining  them  is  not  one  the  results  of  which  are  confirmed 
by  practice.  All  asphalts  are  attacked  by  water  under  certain 
environments  and  some  more  than  others  under  certain  laboratory 
conditions.  In  practice,  however,  the  results  obtained  in  the 
laboratory  are  not  confirmed  if  the  asphalts  are  employed  so  as 
to  bring  out  their  most  desirable  qualities. 

Bearing  in  mind  all  these  considerations  it  is  not  difficult  to 
form  a  decided  opinion  as  to  the  desirability  of  any  native  bitu- 
men for  the  uses  to  which  it  is  put  in  the  paving  industry. 

1  See  page  460. 


286  THE  MODERN  ASPHALT  PAVEMENT. 

CONCLUSIONS. 

From  the  preceding  data  and  discussion  it  is  very  evident 
that  while  many  native  bitumens  may  be  denominated  asphalt, 
from  an  industrial  point  of  view,  they  possess  no  great  uniformity 
in  their  physical  and  chemical  properties  and  that  some  of 
them  are  far  preferable  to  others  for  paving  purposes.  Some 
of  them  are  extremely  stable  bitumens  while  others  are  more 
or  less  changeable  on  the  application  of  heat.  Some  of  them 
are  hard,  others  are  comparatively  soft.  Some  evolve  gas  on 
heating,  showing  that  they  are  unstable.  Some  lose  on  heating 
a  considerable  amount  of  light  hydrocarbons,  petrolenes,  with 
corresponding  hardening  in  the  consistency  of  the  material.  Some 
asphalts  are  obtainable  in  unlimited  amounts  and  of  great  uni- 
formity in  composition.  Others,  while  obtainable  in  large  amounts, 
are  very  variable  in  their  consistency,  the  character  of  no  two 
shipments  corresponding  in  this  respect.  Some  asphalts,  such  as 
those  which  are  obtained  by  collecting  the  exudation  from  maltha 
springs,  are  not  only  very  variable  in  their  character  but,  being 
still  in  a  state  of  transformation  from  maltha  to  asphalt  and, 
therefore,  not  in  equilibrium,  are  unsatisfactory  materials  for  use 
in  the  paving  industry  or  require  such  great  skill  or  judgment  in 
their  treatment  as  to  make  it  difficult  to  construct  good  work 
with  them. 

From  the  results  of  the  author's  experience  with  all  the  bitu- 
mens which  have  been  used  in  the  construction  of  asphalt  pave- 
ments during  the  last  eighteen  years  the  conviction  has  been 
forced  upon  him  that  none  of  them,  with  the  exception  of  gilsonite, 
which  has  recently  proved  itself  under  service  tests  to  be  a  very 
desirable  material,  is  as  uniformly  satisfactory  as  that  obtained 
from  the  Trinidad  pitch  lake,  and  for  the  following  reasons: 

1.  The  available  supply  is  unlimited. 

2.  The  supply  is  of  great  uniformity,  as  appears  from  data 
given  in  the  preceding  pages. 

3.  Asphalt  cements  prepared  from  Trinidad  lake  asphalt  and 
stable  flux  are  less  liable  to  change  in  consistency  when  main- 
tained in  a  melted  condition  at  high  temperatures  for  any  con- 
siderable length  of  time  or  on  being  tossed  about  in  a  mixer  with 


COMPARISON  OF  VARIOUS  NATIVE  ASPHALTS. 


287 


excessively  hot  sand,  something  that  unfortunately  happens  too 
frequently,  than  one  derived  from  any  other  form  of  bitumen. 

4.  It  is  less  susceptible  to  changes  in  consistency  at  extremes 
of  temperature  than  any  other  native  bitumen  which  is  now  used 
extensively  in  the  construction  of  asphalt  pavement. 

5.  The  relation  of  malthenes  to  asphaltenes  is  such  that  the 
proportion  of  flux  which  is  necessary  to  produce  an  asphalt  cement 
of  normal  consistency  is  not  excessive. 

6.  The  mineral  matter  which  it  contains  is  of  a  nature  most 
suitable  to  play  the  role  of  a  filler  and  it  is  mixed  by  nature  with 
the  bitumen  in  a  way  that  it  is  impossible  to  imitate  by  adding 
finely  powdered  mineral  matter  to  a  purer  form  of  bitumen. 

Trinidad  mixtures,  when  the  mineral  aggregate  is  properly 
graded  and  regulated,  are  not  attacked  by  water  to  any  greater 
extent  on  the  street  than  mixtures  made  with  other  asphalts.  In 
fact  surface  mixtures  of  Trinidad  asphalt  resist  impact  more  sat" 
isfactorily  after  three  months  exposure  to  running  water  than 
those  made  with  Bermudez  asphalt,  as  shown  by  the  following 
figures: 

IMPACT  TESTS  OF  ASPHALT  SURFACE  MIXTURES. 


New 

York. 

Trinidad. 

Bermudez. 

2.24 

2.24 

Number  of  blows  : 

21-20 

16-14 

After  3  months'  exposure  to  running  water  
Water  absorbed: 

20 
.129 

13 
.157 

Bermudez  asphalt  possesses  the  disadvantage  that  it  is  far  from 
uniform  in  character,  that  the  bitumens  of  which  it  consists  are 
susceptible  to  volatilization  at  high  temperature  with  a  resulting 
hardening  of  the  material,  as  for  example  when  it  is  mixed  with 


288  THE  MODERN  ASPHALT  PAVEMENT. 

very  hot  sand ;  that  is  to  say,  it  does  not  form  an  asphalt  cement 
which  can  be  maintained  at  high  temperatures  or  mixed  with 
sand  at  high  temperatures  satisfactorily  and  for  this  reason  cannot 
be  used  in-  cold  weather,  and  because  it  is  deficient,  in  com- 
parison with  Trinidad  asphalt,  in  mineral  matter  forming  a  natural 
filler.  As  has  already  been  shown,  surface  mixtures  made  with 
Bermudez  asphalt  are  more  deteriorated  by  the  continued  action 
of  water,  as  far  as  their  resistance  to  impact  is  concerned,  than 
those  made  with  Trinidad  asphalt. 

Maracaibo  asphalt  is  not  a  normal  asphaltic  bitumen  and 
possesses  characteristics  which  throw  a  doubt  upon  its  suitability 
for  the  preparation  of  a  paving  cement,  which  can  only  be  removed 
by  a  study  of  its  behavior  after  a  long  period  of  years  in  actual 
practice. 

Mexican  asphalts  are  far  from  uniform  and  possess  the  same 
disadvantages  that  pertain  to  Bermudez  asphalt.  Their  use  would 
involve  greater  care  and  skill  than  any  of  the  materials  that  have 
been  mentioned. 

Cuban  asphalts  are  very  hard  materials,  approaching  grahamite 
in  composition,  and  must  be  fluxed  with  very  large  proportions 
of  asphaltic  oil.  Their  value  as  paving  materials  has  never  been 
satisfactorily  demonstrated. 

The  solid  residuals  from  asphaltic  or  semi-asphaltic  oils  are 
far  from  uniform  and  are  generally  somewhat  damaged  or  cracked 
in  the  course  of  their  preparation.  The  closest  scrutiny  of  these 
materials  in  the  laboratory  and  the  greatest  skill  in  handling  them 
is  necessary  to  enable  them  to  be  used  satisfactorily  in  the  con- 
struction of  asphalt  surface  mixture. 

Gilsonite  has  now  been  submitted  to  sufficient  service  test 
to  show  that  as  a  paving  cement  it  is  equal  in  character  to  any 
asphalt  in  use  for  this  purpose.  A  pavement  was  laid  with  it 
in  1903  on  Missouri  Avenue,  Main  to  Delaware,  Kansas  City, 
Mo.,  under  the  author's  direction,  and  it  has  proved  entirely 
satisfactory.  Since  that  time  it  has  been  used  equally  successfully 
to  a  large  extent  in  other  cities.  Gilsonite  may  therefore  be 
added  to  the  list  of  those  bitumens  which  are  entirely  suitable 
for  paving  purposes,  if  properly  handled.  This,  of  course,  means 


COMPARISON    OF    VARIOUS  NATIVE    ASPHALTS.        289 

that  the  material  shall  be  fluxed  with  an  asphaltic  oil,  as  a  paraffine 
flux  is  entirely  incompatible  with  the  material. 

The  preceding  criticisms  of  the  various  asphalts  which  have  been 
used  in  the  construction  of  asphalt  pavements  lead  at  once  to  the 
conclusion  that  Trinidad  lake  asphalt  or  gilsonite  is  the  best 
for  this  purpose.  In  the  author's  mind  there  is  no  reasonable 
doubt  that  this  conclusion  is  correct.  It  is  not  intended,  how- 
ever, to  assert  that  satisfactory  pavements  cannot  be  constructed 
from  the  other  asphalts,  especially  where  the  latter  are  not  sub- 
jected to  trying  environment  or  a  heavy  traffic  and  where  con- 
siderable skill  is  exercised  in  their  use.  It  is  asserted,  however, 
that  with  Trinidad  asphalt  there  is  greater  probability  that  a 
pavement  constructed  with  it  will  be  satisfactory,  taking  into 
account  the  fact  that  a  greater  or  less  lack  of  care  is  inevitable 
in  preparing  an  asphalt  surface  mixture  from  any  bitumen.  Trini- 
dad asphalt  will  stand  more  abuse  than  any  other  material  with 
which  we  are  acquainted,  and  on  this  account  is  to  be  strongly 
recommended,  as  well  as  because  less  skill  is  required  in  handling  it. 

SUMMARY. 

In  this  Chapter  there  is  outlined  the  characteristics  which  make 
any  solid  native  bitumen  available  and  desirable  for  paving  pur- 
poses. These  characteristics  are  as  follows: 

1.  The  quantity  available. 

2.  Its  uniformity  in  character. 

3.  Its  stability  in  a  melted  condition  at  high  temperatures. 

4.  Its  stability  in  consistency  at  the  extremes  of  temperature 
which  it  meets  in  an  asphalt  pavement. 

5.  The  proportion  of  malthenes  to  asphaltenes  which  it  con- 
tains. 

6.  The  proportion  of  flux  which  is  required  to  make  an  asphalt 
cement. 

7.  Mineral  matter  present  and  its  character. 

It  appears  that  Trinidad  lake  asphalt  and  gilsonite  fulfil  more 
of  the  necessary  requirements  than  any  other  commercial  supplies 
of  native  bitumen  for  the  purpose  of  constructing  asphalt  pave- 
ments. 


290  THE  MODERN  ASPHALT  PAVEMENT. 

It  also  appears  that  properly  constructed  surface  mixtures 
made  with  Trinidad  lake  asphalt  are  no  more  acted  upon  by  water 
than  those  made  with  other  asphalts,  and  that  the  charge  that 
they  are  acted  upon  to  a  greater  extent  is  dependent  purely  upon 
laboratory  experiments  without  regard  to  making  the  conditions 
under  which  they  are  carried  on  conform  to  tnose  which  are  met 
with  on  the  street. 


PART  IV. 
TECHNOLOGY  OF  THE  PAVING  INDUSTRY. 


CHAPTER  XV. 
REFINING  OF  SOLID  BITUMENS. 

ASPHALTS  which  contain  water  as  they  occur  in  nature  must 
be  freed  from  it  before  they  are  in  a  condition  to  be  used  in  the 
paving  industry.  The  process  of  bringing  this  about  is  called 
refining.  It  really  is  nothing  more  than  some  method  of  drying  the 
asphalt,  in  some  cases  removing  the  more  volatile  hydrocarbons, 
the  loss  of  which,  at  a  later  period,  from  the  asphalt  cement 
would  make  the  latter  of  unstable  consistency,  and  skimming  off 
any  vegetable  matter  which  may  rise  to  the  surface  of  the 
melted  material.  The  process  was  originally  called  refining 
because,  before  the  value  of  the  fine  mineral  matter  was  un- 
derstood, much  of  this  was  separated  out  by  subsidence 
from  the  melted  bitumen  and  the  resulting  asphalt  was  actually 
refined,  having  been  made  purer  or  richer  in  bitumen.  To-day 
the  refining  goes  no  further  than  the  removal  of  such  organic 
contamination  as  may  rise  to  the  surface  of  the  melted  asphalt 
after  the  water  has  been  evaporated,  and  the  volatile  hydrocar- 
bons have  gone  off  with  the  steam,  and  the  thorough  mixing  of 
the  residual  mass  to  a  condition  of  uniformity  in  composition, 
the  mineral  matter  being  maintained  for  this  purpose  in  suspen- 

291 


292  THE  MODERN  ASPHALT  PAVEMENT  . 

sion,  in  the  meanwhile,  by  agitation  of  the  melted  material  in 
any  convenient  way. 

The  drying  process  is  conducted  in  two  different  ways.  The 
material  is  filled  into  an  iron  tank  or  melting-kettle  which  is  heated 
by  a  free  fire,  the  bottom  of  the  kettle  being  protected  by  an  arch 
of  brick;  or  a  large  rectangular  tank  is  used,  the  interior  of  which 
is  filled  with  gangs  of  pipe  through  which  steam  is  conducted  at 
such  a  pressure  as  to  raise  the  asphalt  to  the  same  temperature 
that  is  produced  over  the  free  flame  but  without  any  danger  of 
exceeding  the  highest  temperature  which  the  pressure  of  the 
steam  will  yield.  Fig.  18.1  In  either  case,  since  convection  in 
such  a  viscous  mass  is  very  slow,  agitation  is  carried  on  with  either 
a  current  of  air  or  steam,  in  the  latter  case  the  current  not  being 
admitted  until  the  asphalt  is  melted  and  exceeds  the  boiling-point 
of  water,  this  being  necessary  to  prevent  condensation  and  sub- 
sequent foaming.  The  temperature  must,  of  course,  be  raised 
slowly  at  first  to  avoid  foaming  when  the  bitumen  melts  easily 
and  the  asphalt  contains  much  water.  When  the  temperature 
has  been  raised  to  a  point  where  the  material  is  thoroughly  melted 
and  steam  is  no  longer  given  off  the  process  is  finished  and  the 
refined  asphalt  is  ready  to  be  drawn  off.  The  details  of  this  process 
are  ones  purely  of  economy,  the  object  being  to  dry  and  get  the 
asphalt  into  packages  suitable  for  handling.  Where  the  material 
is  to  be  made  into  cement  and  used  on  the  spot,  the  latter 
is  unnecessary.  The  packages  are  usually  old  hydraulic  cement 
barrels  which  before  use  are  clayed  on  the  inside  by  being  re- 
volved in  a  bath  of  clay  and  water.  The  claying  is  done  to  make 
it  possible  to  strip  the  staves  from  the  asphalt  more  easily  when 
preparing  it  at  its  destination  to  be  made  into  cement  and  to  do 
this  with  the  loss  of  the  least  possible  amount  of  asphalt  adherent 
to  the  staves. 

In  the  fire  refining  method  four  or  five  days  are  required  to 
complete  the  operation.  In  refining  solid  bitumens  in  this  way 
danger  is  always  incurred  of  overheating  them,  with  the  formation 
of  coke  and  the  cracking  of  the  hydrocarbons.  There  is  a  certain 
formation  of  coke  in  all  cases  where  a  direct  flame  is  in  use  and 

1  Page  405. 


REFINING  OF   SOLID  BITUMENS.  293 

that  some  asphalts  are  injured  during  the  process  is  shown  by  the 
fact  that  the  resulting  bitumen  is  not  entirely  soluble  in  cold  car- 
bon tetrachloride.  To  avoid  such  difficulties  a  very  thorough 
mechanical  or  other  form  of  agitation  is  absolutely  essential. 

By  the  steam  process  the  refining  is  completed  in  24  hours 
or  less  without  any  danger  of  injury  to  the  bitumen  from  over- 
heating. The  agitation  in  this  process  is  generally  by  means  of 
dry  steam.  The  use  of  steam  results  in  the  volatilization  of  a 
rather  larger  amount  of  lighter  oils  than  occurs  with  air  agitation 
and  it  may  be  possible,  for  this  reason,  that  it  could  be  replaced  by 
air  beneficially,  although  hot  air  has  a  decidedly  strong  effect  upon 
native  bitumens  as  has  been  shown  in  connection  with  the  con- 
densed oils.1 

From  ten  to  twenty-five  or  more  tons  are  refined  at  once,  the 
larger  amounts  by  the  steam  process,  and  the  temperature  reached 
is  about  325°  F. 

Almost  all  asphalts  require  refining  but  some  other  native 
bitumens  which  can  be,  and  are,  used  to  a  small  extent  in  the 
paving  industry,  are  anhydrous  and  need  no  drying.  Gilsonite  and 
grahamite  need  no  refining,  being  practically  dry  and  pure  bitu- 
mens. 

The  Preparation  of  the  Asphalt  Cement. — Whatever  solid 
bitumen  and  flux  are  selected  for  the  purpose,  their  careful  com- 
bination is  necessary  for  the  preparation  of  a  satisfactory  asphalt 
cement.  The  carefully  weighed  asphalt  is  melted  and  raised  to 
a  temperature  of  about  300°  or  325°  F.,  or  if  the  material  is  taken 
on  the  immediate  completion  of  refining,  as  happens  where  a 
refinery  and  paving  plant  are  associated,  it  is  carefully  gauged. 
The  flux,  having  preferably  been  heated  with  steam  coils  in  the 
receptacle  containing  it  to  150°  to  200°  F.,  is  then  slowly  run  into 
the  melting-tank  holding  the  asphalt,  agitation  with  air  or  steam 
having  been  established,  the  air  or  steam  being  admitted  through 
lines  of  pipe,  perforated  with  frequent  openings  and  which  lie  along 
the  bottom  of  the  tank.  A  satisfactory  and  sufficient  agitation 
is  most  essential  and  steam  has  been  found  more  suitable  than 
air  where  its  use  is  possible.  It  should,  of  course,  be  high  pressure 

1  See  page  273. 


294  THE  MODERN  ASPHALT  PAVEMENT. 

steam  and  it  should  not  be  admitted  to  the  melted  asphalt  until 
the  latter  is  at  such  a  temperature  as  to  prevent  condensation. 
Every  provision  should  also  be  made  that  the  steam  be  quite  dry 
by  blowing  all  condensed  water  out  of  the  pipes  carrying  it.  Neg- 
lect to  do  this  will,  otherwise,  cause  dangerous  foaming.  A  check- 
valve  should  also  be  provided  at  a  point  above  the  surface  of  the 
melted  asphalt  to  provide  for  the  admission  of  air  when  the  steam 
is  shut  off  and  prevent  condensation  and  the  production  of  a 
vacuum  which  will  draw  the  melted  asphalt  cement  back  into 
the  agitation  pipes  and  clog  them.  Air  agitation  is  simple  and 
fairly  satisfactory  but  the  effect  of  blowing  hydrocarbon  oils 
with  air  results  in  hardening  them  and  changing  their  consistency 
in  a  marked  degree  and  on  that  account  is  undesirable. 

The  agitation,  of  whatever  kind,  should  be  kept  up  until  the 
solid  bitumen  and  liquid  flux  are  thoroughly  mixed  and  in  homo- 
geneous solution.  The  length  of  time  required  will  depend  on  the 
force  of  the  current  of  steam  or  air  and  the  character  and  tem- 
perature of  the  melted  materials.  Under  the  most  favorable 
circumstances  three  hours  are  requisite  and  with  inferior  agita- 
tion eight  or  more  may  be  necessary. 

To  the  eye  of  the  experienced  yard  foreman  the  point  at  which 
the  combination  is  complete  and  the  mixture  homogeneous  will 
be  evident,  but  the  material  can  be  tested  by  pouring  some  of  it 
into  a  pail  of  cold  water  and  examining  it  on  cooling  Any  oili- 
ness  is  a  sign  that  more  agitation  is  necessary. 

The  asphalt  cement  having  been  found  to  be  homogeneous 
the  next  step  is  the  determination  of  the  fact  that  the  consistency 
is  that  which  is  desired.  This  can  be  arrived  at  in  various  ways 
of  greater  or  less  refinement.  The  ordinary,  and  always  the  pre- 
liminary test,  is  that  of  chewing  a  small  piece  of  the  cement 
cooled  by  pouring  it  into  cold  water.  On  putting  the  cement 
in  the  mouth  and  working  it  between  the  teeth  it  rapidly  assumes 
the  temperature  of  the  mouth  which  is  a  very  uniform  one,  that 
of  the  normal  temperature  of  the  body,  98.4°  F.  The  amount 
of  work  that  is  done  by  the  jaws  upon  the  cement  will  readily 
show  whether  it  is  harder  or  softer  than  what  experience  has 
taught  to  be  a  proper  consistency  and  it  is  not  difficult  for  one 


REFINING  OF  SOLID  BITUMENS.  295 

who  makes  this  test  daily  to  decide  whether  the  asphalt  in  ques- 
tion is  within  four  or  five  points  of  the  consistency  desired  and 
registered  by  the  more  accurate  penetration  machine.  In  experi- 
enced hands  it  is  questionable  whether  a  more  accurate  test  is 
absolutely  necessary,  except  as  a  matter  of  record. 

A  more  refined  test  which  is  available  for  use  by  the  yard  fore- 
man at  the  plant  is  that  known  as  a  flow  test  which  permits,  ac- 
cording to  a  method  described  in  Chapter  XX  VIII  of  comparing  the 
relative  flow,  at  temperatures  above  the  softening  point  of  the 
cement,  of  the  material  to  be  tested  with  that  of  a  standard  of 
the  desired  consistency  prepared  in  the  laboratory. 

Where  a  definite  determination  is  required  for  purposes  of 
record  one  of  the  several  penetration  machines  may  be  used,  but 
these  require  careful  manipulation  and  their  use  sometimes  neces- 
sitates greater  refinement  than  a  yard  foreman  is  capable  of. 

Under  any  circumstance  it  is  absolutely  necessary  that  the 
consistency  of  the  asphalt  cement  shall  be  so  regulated  that  it 
will  be  entirely  uniform  for  any  one  piece  of  work.  What  this  con- 
sistency shall  be  will  depend  upon  the  character  of  the  work  which 
is  being  done  and  upon  its  environment,  both  as  to  traffic  and 
climate.  The  variations  in  this  respect  will  be  discussed  later. 

If  the  cement  is  to  be  held  in  a  melted  condition  for  any  length 
of  time  agitation  must  be  maintained,  especially  if  it  contains 
mineral  matter.  The  purer  native  bitumens  and  residues  from 
asphaltic  petroleums  require  very  little  beyond-  that  necessary  to 
prevent  any  one  portion  remaining  for  any  great  length  of  time  in 
contact  with  the  source  of  heat,  whether  the  walls  of  a  tank  heated 
by  direct  flame  or  the  steam  coils.  All  cements  can  be  allowed  to 
become  solid  and  cold  if  they  are  thoroughly  agitated  again  on 
remelting.  On  the  other  hand  too  powerful  agitation  is  injurious 
as  it  volatilizes  the  lighter  portions  of  the  cement  and  hardens  it. 
Continued  agitation  with  air  has  a  marked  effect  upon  the  charac- 
ter of  all  oils  by  the  extraction  of  hydrogen  and  condensation  of 
the  hydrocarbons  to  a  short  rubbery  solid  such  as  the  blown  petro- 
leum now  to  be  found  on  the  market  as  an  article  of  commerce, 
and  which  has  been  already  described.  The  result  of  continued 
air  agitation,  therefore  is  to  harden  an  asphalt  in  two  ways,  by 


296  THE  MODERN  ASPHALT  PAVEMENT. 

the  volatilization  of  the  lighter  oils  and  also  by  increasing  their 
density  by  condensation  of  two  molecules  into  one.  Steam  hardens 
a  cement  only  by  the  volatilization  of  the  lighter  constituents. 
Steam  is,  therefore,  probably  preferable  for  the  agitation  of  a  fin- 
ished asphalt  cement,  although  air  may  be  more  desirable  as  a 
means  of  agitation  during  refining. 

The  actual  changes  which  take  place  with  different  fluxes  and 
different  asphalts  will  be  shown  further  on. 

Character  of  Various  Asphalt  Cements. — The  character  of  an 
asphalt  cement  depends  upon  that  of  the  solid  bitumen  and  of 
the  flux  from  which  it  is  prepared. 

Asphalt  cements  may  be  divided  into  several  classes. 

1.  Those  composed  of  the  standard  solid  native  bitumens,  such 
as   Trinidad   and   Bermudez   asphalts,    and   paraffine   petroleum 
residuum. 

2.  Those  composed  of  the  same  asphalts  and  fluxes  or  residuums 
from  asphaltic  petroleums. 

3.  Those  made  from  the  same  asphalts  and  fluxes  which  are 
mixtures  of  asphaltic  and  paraffine  oils. 

4.  Those  made  from  other  solid  native  bitumens  and  asphaltic 
fluxes. 

5.  Those  composed  of  solid  residual  bitumens  from  asphaltic 
petroleum  brought  to  a  proper  consistency  with  residuum  of  the 
same  origin. 

6.  Any  of  the  first  four  classes  with  the  addition  of  small 
amounts  of  the  condensed  or  blown  oil,  or  other  forms  of  bitumen 
not  constituting  one  of  the  main  constituents  of  the  cement. 

Asphalt  Cements  Composed  of  Trinidad  or  Bermudez  and 
Similar  Asphalts  and  Paraffine  Petroleum  Residuum. — Some  years 
ago  there  was  a  popular  prejudice  against  the  use  of  paraffine 
petroleum  residuum  as  a  fluxing  agent  for  asphalt.  This  was  not 
founded  on  the  results  of  any  careful  investigation  or  tangible 
evidence.  It  arose  at  first  from  a  desire  to  find  some  excuse  for 
the  poor  wearing  quality  of  some  carelessly  constructed  asphalt 
pavements  and  from  the  fact  that  the  earlier  surfaces  were  readily 
attacked  by  water  where  subjected  to  its  action  for  any  length  of 
time.  It  was  claimed: 

That  a  part  of  the  residuum  of  paraffine  petroleum  is  soluble  in 


REFINING  OF  SOLID  BITUMENS.  297 

water  and  that  by  the  continued  action  of  the  latter  on  the  oil  in 
the  asphalt  cement,  the  cement  is  deteriorated. 

That  on  standing  in  a  melted  condition  the  petroleum  oil  rises 
to  the  top  of  the  cement  and  can  be  "skimmed  off  like  cream." 

That  the  bitumen  of  Trinidad  and  other  asphalts  are  not  com- 
pletely soluble  in  paraffine  residuum  but  are  only  mechanically 
mixed. 

The  fallacies  in  two  of  these  claims  are  readily  shown. 

That  the  first  is  false  is  shown  by  the  fact  that  distilled  water 
which  has  been  allowed  to  stand  in  a  glass-stoppered  bottle  in 
contact  with  standard  paraffine  residuum  for  four  years  is  as 
bright  and  clean  as  when  first  put  there  and  contains  nothing  in 
solution.1 

The  second  is  equally  wrong  since  a  tank  of  asphalt  cement 
maintained  one  week  at  a  temperature  of  300°  F.,  without  agita- 
tion, on  cooling,  was  not  to  the  slightest  degree  oily  or  greasy  on 
the  surface,  which  would  be  the  case  if  any  oil  had  separated  like 
cream. 

The  proposition  that  the  bitumen  of  Trinidad  and  other  asphalts 
is  not  completely  soluble  in  standard  paraffine  petroleum  residuum 
can  be  equally  well  disproved  and  it  can  be  shown  that  asphaltic 
bitumens  are  as  soluble  in  paraffine  residuum  as  in  the  asphaltic 
oils  of  California.  The  results  of  some  experiments  in  this  direc- 
tion by  the  author  were  presented  in  articles  in  "Municipal 
Engineering  "  for  June,  July  and  August,  1897,  and  for  June,  1899. 
The  experiments  and  conclusions  arrived  at  and  presented  in  the 
latter  article  were,  in  the  main,  as  follows: 

"Three  asphalt  cements,  prepared  with  great  care  and  uni- 
formity, as  appears  from  the  results  of  duplicate  analyses  of  the 
original  material,  were  placed  several  inches  deep  in  glass  tubes 
8  inches  long  and  }  of  an  inch  in  diameter  and  maintained  at  a 
temperature  of  325°  F.  for  three  days,  being  centrifugaled  at  that 
temperature  several  times  to  assist  any  separation  that  might  take 

1  Messrs.  Whipple  and  Jackson  in  a  paper  read  before  the  Brooklyn  En- 
gineers Club  and  published  in  the  Engineering  News  for  March  22,  1900,  have 
shown  that  petroleum  residuum  is  affected  less  by  water  than  any  bitumin- 
ous substance  that  they  examined. 


298 


THE  MODERN  ASPHALT  PAVEMENT. 


"RESULTS   OF   CENTRIFUGAL   ACTION   ON   VARIOUS   ASPHALT 

CEMENTS. 

"100  Ibs.  Trinidad +  20  Ibs.  of  paraffine  residuum. 


Original 
Cement. 
Duplicates. 

Top 
45  Per  Cent. 
Duplicates. 

Bottom 
45  Per  Cent. 
Duplicates. 

Sedi- 
ment, 
10  Per 
Cent. 

'  '  Bitumen  soluble  in  chloroform 

27.6 
26.8 
22.3 

83.2 
16.8 

65.5 
5.4 
0 

Bitumen  soluble  in  CS2  

63.4     63.5 
48.6     48.7 

76.6     76.6 
23.4    23.4 

30.3 
6.3 
55° 

69.9     70.  1 
53.4     53.4 

76.3     76.2 
23.7    23.8 

23.9 
6.2 
49° 

68  .  5      68  .  7 

52.7    52.9 

76.9     77.0 
23.1     23.0 

25.1 
6.4 
51° 

Bitumen  soluble  in  88°  naphtha.  . 
Per  cent  of  total  bitumen  thus  sol- 
uble 

Per  cent  of  total  bitumen  insoluble 

• 

"100  Ibs.  Trinidad  +27 
"Bitumen  soluble  in  chloroform.  . 

'  Ibs.  Califoi 

*nia  'G'  gra 

de  flux. 

27.3 
26.8 
22.5 

84.0 
16.0 

65.8 
7.4 
0 

07.  5 
66.8 
53.9 
80  7 
19.3 

15.0 

8.2 
0 

Bitumen  soluble  in  CS2  .  .  . 

64.7     64.8 
51.1     51.3 

79.0     79.2 
21.0    20.8 

28.9 
6.4 
46° 

-18  Ibs.  of  p 

71.6     71.9 
55.7     56.0 

77.8     77.9 
22.2    22.1 

22.9 
5.5 
47° 

araffine  resi< 

70.2     70.4 
55.1     55.4 

78.5    78.7 
21.5    21.3 

23.0 
6.8 
50° 

iuum. 

Bitumen  soluble  in  88°  naphtha.  .  . 
Per  cent  of  total  bitumen  thus  sol- 
uble 

Per  cent  of  total  bitumen  insoluble 
Mineral  matter.  

Penetration  

"100  Ibs.  Bermudez-f 
"Bitumen  soluble  in  chloroform 

Bitumen  soluble  in  CS2  
Bitumen  soluble  in  88°  naphtha.  . 
Per  cent  of  bitumen  thus  soluble  .  . 
Per  cent  of  total  bitumen  insoluble 

Mineral  matter.  

92.6     92.8 
73.1     73.2 
78.9     78.9 
21.1     21.1 

3.2      3.3 
4.2      3.9 
60° 

96.2     96.4 
74.5     74.7 
77.4     77.5 
22.6     22.5 

1.9 
1.9 

56° 

95.2    95.4 
73.6     73.8 
77.3     77.4 
22.7    22.6 

2.2 
2.6 
55° 

Penetration  at  78°  F.  

REFINING  OF  SOLID  BITUMENS.  299 

place.  On  cooling  the  asphalt  was  divided  into  three  parts;  an 
upper,  45  per  cent;  a  lower,  45  per  cent;  and  the  bottom,  10  per 
cent,  of  sediment.  The  consistency  and  composition  of  these  por- 
tions were  then  determined  by  the  most  careful  methods,  extract- 
ing with  naphtha  and  carbon  disulphide,  filtering  on  a  Gooch  cru- 
cible and  burning  the  bitumen  solution  for  any  inorganic  correction. 
The  results  were  obtained  in  duplicate,  except  in  the  case  of  the 
sediment.  Their  agreement  is  confirmatory  of  their  accuracy.  See 
results  tabulated  on  page  298. 

"These  results  show  that  there  is  no  difference  in  the  char- 
acter of  the  bitumen  in  the  cement  made  from  Trinidad  asphalt 
and  residuum  in  the  two  portions  of  cement  above  the  residue, 
after  heating  and  subsidation,  from  that  of  the  original  material. 
With  California  oil  and  Bermudez  asphalt  there  is  a  slight  loss  of 
oil  in  the  upper  portions  and  consequent  small  reduction  in  the 
percentage  of  naphtha  soluble  bitumen.  In  the  sediments  the  pro- 
portion of  naphtha  soluble  to  total  bitumen  has  increased  in  all 
three  cements.  The  fact  that  something  in  the  cement  more  solu- 
ble in  naphtha  and  heavier  than  the  ordinary  constituents  has  been 
thrown  down,  is  peculiar." 

What  this  is  it  is  impossible  to  say  at  present,  but  it  appears 
from  a  paper  by  R.  P.  Van  Calcar,  which  has  recently  appeared  in 
the  Recueil  des  Travaux  Chimiqices  des  Pays-Bas,1  that  where  solu- 
tions of  various  salts  in  water  were  subjected  to  a  centrifugal  force 
400  times  that  of  gravity  they  became  more  concentrated  at  the 
periphery  after  a  few  hours,  contrary  to  the  preconceived  ideas  that 
the  molecules  in  a  true  solution  were  unaffected  by  gravity,  and 
hence  were  in  a  different  state  from  those  in  colloidal  solutions. 
As  a  consequence  of  Van  Calcar  s  conclusions  the  results  obtained 
with  the  asphalt  cement  are  not  unexpected. 

"As  a  whole  the  results  seem  to  the  writer  to  refute  the  state- 
ments which  have  been  made  in  regard  to  residuum  and  to  show 
that  90  per  cent  of  the  asphalt  cement  made  of  Trinidad  lake 
asphalt  and  residuum  was  unchanged  to  any  perceptible  degree 
after  the  severe  treatment  it  had  been  subjected  to  by  standing 
and  centrifugaling  at  a  high  temperature,  while  any  changes  that 
1  Science,  1904,  August  19,  20,  250. 


300 


THE  MODERN  ASPHALT  PAVEMENT. 


took  place  in  the  sediment  were  found  as  well  in  cements  made 
with  the  California  residuum  or  so-called  asphaltic  flux." 

As  a  matter  of  fact  there  is  no  evidence  to  show  that  there  is 
any  essential  difference  between  the  California  fluxes  and  paraffine 
residuums  in  their  power  of  dissolving  the  bitumen  of  Trinidad  and 
Bermudez  asphalts,  or  that  the  latter  is  not  a  satisfactory  flux, 
on  this  account,  for  making  asphalt  cements  with  these  asphalts. 
The  successful  use  of  it  in  many  pavements  laid  twenty  years  ago, 
which  are  now  in  perfect  repair,  is  the  best  evidence  that  it  is 
satisfactory. 

Amount  of  Residuum  Necessary  in  Making  An  Asphalt  Ce- 
ment.— The  amount  of  paraffine  residuum  oil  which  it  is  necessary 
to  use  per  100  pounds  of  Trinidad  or  Bermudez  asphalt  to  make  a 
cement  of  satisfactory  consistency  depends  on  the  character  of 
this  flux.  It  may  be  very  variable,  but  with  a  standard  material 
should  not  vary  more  than  4  pounds  per  hundred  of  the  asphalt. 
With  some  less  carefully  prepared  residuums  the  difference  may  be 
6  pounds.  For  example  the  oil  in  use  by  one  company  in  1899 
and  by  another  in  1898  had  the  following  characteristics:  . 


Residuum 

Light 

Heavy 

Specific  gravity,  78°  F./780  F.,  orig.  mat.,  dry 
Beaum6        

.9197 

22.7° 

.9331 
20.5° 

Flashes,  °  F  

330°  F. 

442°  F. 

Loss,  400°  F.,  7  hours  

17.3 

3.8% 

Pounds  per  100  of  asphalt  to  make  asphalt 
cement  of  60°  penetration: 
Trinidad  lake     

16 

22 

Bermudez  1899  

14 

23 

Much  less  of  the  lighter  oil  would  produce  the  same  softening 
effect  as  the  larger  quantity  of  the  heavier  residuum.  It  becomes 
a  question  then  to  determine  as  far  as  possible  which  is  the  most 
desirable  cement  and  the  only  evidence  that  is  available  are  the 
results  of  an  examination  of  the  two  cements  as  to  the  change  in 
their  consistency  at  such  extremes  of  temperature  as  are  common 
in  pavements  and  as  to  their  change  in  penetration  on  being  main- 


REFINING    OF    SOLID    BITUMENS. 


301 


tained  in  a  melted  condition  for  some  time.    Experiments  in  these 
directions  furnish  the  following  information: 

COMPARISON  OF  CONSISTENCY  OF  ASPHALT  CEMENTS  AT  DIF- 
FERENT TEMPERATURES  WHEN  MADE  WITH  DIFFERENT 
FLUXES. 


Asphalt. 

Residuum. 

Pounds 
per  100 

Penetration  al 

of  Asphalt. 

45°  F. 

78°  F. 

100*  F. 

Bermudez  
« 

Light 
Heavy 

14 
23 

30° 
32 

60° 
60 

105° 
125 

Trinidad.  

Light 

16 

29 

65 

120 

M 

Heavy 

22 

29 

63 

115 

PENETRATION  AND  LOSS  AFTER  HEATING  TO  300°  FAHR. 


Penetration  at  78°  F. 

Loss. 

23: 

After 
Heating 
4  Hours 

After 
Heating 
6  Hours 

1st 
2  Hours 

2d 
2  Hours 

3d 

2  Hours 

TotaL 

Bermudez.  .  . 

Light 

60° 

36° 

30° 

1.36% 

.79% 

.71% 

2.86% 

« 

Heavy 

60 

50 

45 

.50 

.40 

.30 

1.20 

Trinidad.  .  .  . 

Light 

65 

35 

30 

1.56 

.75 

.58 

2.89 

M 

Heavy 

63 

40 

38 

.98 

.34 

.33 

1.65 

At  temperatures  between  78°  and  45°  F.  there  is  no  great 
difference  in  the  penetration  of  cements  made  with  heavy  and 
light  residuum.  At  higher  temperatures  there  is  a  considerable 
but  not  constant  difference.  In  the  case  of  Bermudez  cements, 
that  made  with  the  heavy  oil  is  softer  at  100°  because  of  the 
greater  softening  effect  of  the  larger  amount  of  flux,  23  pounds, 
as  compared  to  14  of  the  lighter  oil,  while  with  the  harder  Trinidad 
the  reverse  is  the  case.  As  will  be  seen  later,  a  flux  which  is  so 
dense  that  an  excess  of  it  is  required  to  produce  a  cement  of  normal 
consistency  at  ordinary  temperatures  may  make  a  cement  more 
susceptible  to  high  temperatures  than  a  lighter  or  less  dense  one. 

As  to  the  permanency  of  the  two  classes  of  cement,  however 
the  figures  show  that  on  maintaining  it  in  a  melted  condition, 


502 


THE  MODERN  ASPHALT  PAVEMENT. 


and  of  course  on  mixing  with  hot  sand,  there  is  a  much  larger  loss 
of  oil  and  a  greater  hardening  of  the  cement  fluxed  with  light  than 
with  heavy  residuum.  For  this  reason  alone  cements  made  with 
the  heavier  oil  seem,  up  to  a  certain  point,  decidedly  preferable  to 
those  made  with  the  lighter  forms  in  use.  Determinations  of  the 
consistency  of  the  bitumen  in  old  surfaces  laid  with  cements  made 
with  light  residuum  as  compared  with  others  holding  heavy  oil 
confirm  this.  Surfaces  in  Omaha  were  laid  in  1890  in  part  with  a 
light,  so-called  summer  oil,  and  in  part  with  a  heavy  one.  The 
consistency  of  the  bitumen  in  these  different  surfaces  when  laid 
and  again  on  extraction  was  as  follows: 


Flux  in  Cement. 

Original  Pen. 

Pen.  1899. 

Loss. 

Light 
Heavy 

67° 
50° 

35° 
30° 

32° 
20° 

It  seems  that  the  cement  made  with  the  very  light  oil  has 
hardened,  either  in  the  mixer  or  by  age,  to  a  much  greater  extent 
than  the  other. 

Many  good  pavements  have  been  made  with  the  lighter  fluxes, 
however,  and  it  would  be  unfair  to  condemn  them  entirely,  or  to 
say  that  they  are  necessarily  the  cause  of  defects  in  asphalt  sur- 
faces, but  it  seems  plain  that  the  heavier  oil  is  in  general  the  more 
satisfactory  although  more  of  it  must  be  used. 

In  the  light  of  the  previous  results  no  valid  objection  can  be 
raised  and  maintained  against  the  use  of  a  suitable  paraffine  petro- 
leum residue  as  a  flux  for  Trinided  lake  and  Bermudez  bitumens 
in  the  preparation  of  an  asphalt  cement,  and  this  is  not  surprising 
when  it  is  considered  that  many  million  yards  of  satisfactory 
pavement  have  been  laid  with  such  a  cement. 

Paraffine  residuums  are  to  be  found  on  the  market,  and  this 
was  the  case  very  frequently  in  the  early  days  of  the  industry,  which 
are,  owing  to  the  manner  in  which  they  have  been  prepared,  quite 
unsuitable  for  use,  but  this  has  no  bearing  on  the  question  of  the 
availability  of  standard  material. 

For  fluxing  Trinidad  land  asphalt  and  others  of  a  hard  nature 
paraffine  residuum  is  not  suitable  because  of  the  deficiency  of 


KEFINING    OF    SOLID    BITUMENS.  303 

lighter  malthenes  in  these  asphalts,  the  lack  of  which  is  not  made 
up  by  the  hydrocarbons  of  such  a  residuum. 

Asphalt  Cements  Composed  of  Trinidad  or  Bermudez  and  Simi- 
lar Asphalts  and  Flux  or  Residuum  from  Asphaltic  Petroleums. — 
Trinidad,  Bermudez,  and  other  similar  asphalts  can  be  satisfactorily 
fluxed  with  the  asphaltic  residuums  which  are  prepared  in  the 
East  from  Texas  oil  and  are  now  on  the  market.  The  char- 
acter of  this  residuum  has  already  been  described.  It  is  a 
most  desirable  material  and  can  be  used  in  about  the  same  pro- 
portions and  in  exactly  the  same  way  as  the  paraffine  petroleum 
residuum.  It  should  not,  however,  be  so  dense  as  to  necessitate 
the  use  of  excessive  amounts  of  it,  since  under  these  conditions, 
as  was  shown  to  be  the  case  with  paraffine  residuum,  the  resulting 
asphalt  cement  will  be  too  susceptible  to  high  temperatures.  The 
density  should  be  such  that  not  more  than  22  pounds  of  oil  per 
100  of  refined  Trinidad  or  of  Bermudez  asphalt  shall  be  required 
to  produce  a  cement  of  65°  penetration  on  the  Bo  wen  machine. 
Such  an  oil  will  have  a  density  of  .95.  The  heavier  residuum  of 
a  density  of  .97,  also  found  on  the  market,  is  not  satisfactory, 
although  this  flux  has  its  use  with  certain  other  native  bitumens. 

Comparing  the  general  characteristics  and  stability  of  the 
two  forms  of  residuum  it  has  been  found  and  confirmed  by  prac- 
tical experience  that  there  is  probably  a  slight  preference  in  favor 
of  a  not  too  dense  asphaltic  flux,  but  this  difference  is  not  sufficiently 
great  to  make  it  obligatory  to  use  the  latter  except  in  work  of  the 
very  highest  character  on  streets  which  carry  very  heavy  traffic 
and  where  it  is  certain  that  the  character  of  the  asphaltic  will 
be  as  uniform  and  satisfactory  as  that  of  the  paraffine  flux,  and 
unfortunately  this  is  not  always  the  case.  The  greatest  care  is 
necessary  in  its  preparation,  as  any  overheating  or  cracking  in  the 
latter  will  result  in  the  presence  of  light  oils  which  volatilize  readily 
and  cause  a  rapid  change  in  the  consistency  of  the  cement,  while 
maintaining  it  in  a  melted  condition  or  during  the  time  that  the 
cement  is  being  tossed  about  in  the  mixer  in  contact  with  hot 
sand  during  the  preparation  of  surface  mixture.  It  is  possible, 
therefore,  that  in  comparison  with  an  asphaltic  flux  of  inferior 
grade  a  paraffine  residuum  may  be  preferable. 


304  THE  MODERN  ASPHALT  PAVEMENT. 

Combinations  of  Trinidad,  Bermudez,  and  similar  asphalts  with 
the  heavy  California  flux  known  as  No.  2  or  G  grade  are  not  satis- 
factory, since  the  proportion  of  such  a  flux  to  the  asphalt  in  order 
to  produce  a  cement  of  proper  consistency  is  so  large,  being  in  the 
neighborhood  of  60  pounds  of  flux  to  100  of  Trinidad  asphalt,  that 
the  resulting  material  is  excessively  susceptible  to  high  tempera- 
tures. Such  combinations  are,  therefore,  rarely  used.  Where 
the  solid  asphalt  is  one  that  has  been  much  hardened  by  age  or 
exposure,  as  in  the  case  of  that  from  La  Patera  in  California,  a 
supply  of  which  is  no  longer  on  the  market,  the  mine  being  ex- 
hausted, the  use  of  a  heavy  California  flux  or  a  very  dense  Texas 
residuum  is  imperative,  at  least  as  a  preliminary  fluxing  material, 
to  supply  the  lack  of  denser  malthenes  in  the  asphalt.  If  a  certain 
amount  of  this  flux  is  used,  however,  the  remainder  can  be  of  a 
lighter  form,  and  probably  preferably  so.  Asphalts  of  this  descrip- 
tion are  not  at  present  of  commercial  interest,  with  the  exception; 
perhaps,  of  that  obtained  in  Cuba  from  the  Bejucal  mine. 

Asphalt  cements  have  sometimes  been  made  from  the  solid 
native  bitumens,  including  the  asphalts,  and  the  natural  malthas. 
Pavements  constructed  with  asphalt  cements  made  in  this  way 
have  proved,  however,  to  be  unsatisfactory.  Some  experiments 
were  conducted  some  years  ago  by  the  writer  to  determine  why 
such  asphalt  cements  were  not  satisfactory. 

In  the  laboratory  it  was  found  that  the  solubility  of  the  bitu- 
mens of  Trinidad  and  Bermudez  asphalts  was  as  great  in  the 
ordinary  malthas  as  in  the  residuums  from  paraffine  and  asphaltic 
petroleums.  There  was  no  preference  in  this  respect.  When, 
however,  the  permanence  of  consistency  of  malthas  when  exposed 
to  heat  was  compared  with  that  of  residuums,  there  was  found 
originally  to  be  a  great  deficiency  in  that  of  the  malthas. 

Residuum  such  as  is  at  present  in  use  has  already  been  shown 
to  volatilize  but  a  small  amount  when  heated  in  an  open  dish 
in  a  bath  kept  at  400°  F.  for  7  hours,  and  to  remain  of  the  same, 
or  very  nearly  the  same,  consistency  after  as  it  was  before  heating. 
The  desirable  features  of  a  carefully  prepared  residuum  as  a  soften- 
ing agent  are  not  lost  on  continued  heating,  nor  is  there  sufficient 


REFINING    OF    SOLID    BITUMENS.  305 

oil  volatilized  at  the  high  temperatures  at  which  asphalt  cement 
is  maintained  in  a  melted  condition,  with  agitation  for  consider- 
able periods  of  time  in  large  masses,  to  change  the  consistency 
to  any  marked  degree.  As  an  example,  a  Trinidad  lake  asphalt 
cement  made  on  February  29,  1896,  by  mixing  100,000  pounds 
of  refined  asphalt  with  20,000  pounds  of  residuum  had  a  pene- 
tration of  55°.  It  was  held  over  a  very  low  fire  in  a  melted  con- 
dition for  48  hours  and  then  had  changed  in  consistency  so  little 
as  to  penetrate  49°.  After  73  hours  melting  the  penetration  was 
46°.  This  is  an  extremely  small  change  for  such  a  considerable 
length  of  time. 

Asphalt  cements  made  with  the  native  malthas  behave  quite 
differently.  On  heating  for  any  considerable  tune  they  are  con- 
verted into  hard  and  glassy  pitches  by  volatilization  of  oil,  and, 
perhaps,  by-  condensation  of  its  hydrocarbon  constituents.  Such 
material  is  unstable  and  cannot  form  a  cement  which  can  be 
maintained  at  a  uniform  consistency. 

On  Saturday,  February  29,  1896,  in  the  early  morning,  500 
pounds  of  Bakersfield  maltha  was  added  to  2000  pounds  of  refined 
Trinidad  asphalt,  or  at  the  rate  of  25  pounds  to  the  100.  After 
agitation  the  resulting  asphalt  cement  penetrated  55°.  It  was 
allowed  to  stand  with  a  low  fire  until  the  following  Monday  morn- 
ing, March  2.  The  penetration  had  then  fallen  to  25°.  On  stand- 
ing another  24  hours  the  penetration  was  found  to  be  22°.  270 
pounds  of  additional  maltha  was  then  added,  corresponding  to 
13.5  pounds  per  100,  whi^h,  after  agitation,  raised  the  penetration 
to  54°.  After  4  hours  of  heating  and  agitation  a  sample  was 
taken  and  found  to  penetrate  but  35°. 

It  appears  from  this  experiment  that  the  light  native  Cali- 
fornia malthas  are  not  suitable  for  the  preparation  of  an  unchange- 
able cement.  Why  this  is  so  can  be  seen  in  the  results  of  an  exam- 
ination of  the  maltha  in  the  laboratory.  While  it  is  thick  enough 
to  require  5  pounds  more  of  it  to  every  100  pounds  of  Trinidad 
refined  asphalt  to  make  a  cement  of  the  same  consistency  that 
is  obtained  with  residuum,  it  loses  on  heating  for  7  hours  to  400°  F. 
20.3  per  cent.  This  light  oil  is,  of  course,  volatilized,  in  the  same 


306  THE  MODERN  ASPHALT  PAVEMENT. 

way,  though  more  slowly,  from  the  asphalt  cement  made  with 
the  maltha,  and  the  loss  causes  the  rapid  fall  in  penetration  and 
hardening  of  the  cement. 

An  experiment  with  one  of  the  asphaltic  oils  extracted  from  the 
abundant  supply  of  asphaltic  sandstone  rock  in  Texas  resulted 
similarly.  The  asphaltic  oil,  or  maltha,  as  received  was  heated  for 
some  time  at  a  low  temperature  to  drive  off  any  water  and  very 
volatile  oil.  A  cement  was  then  made  of  Trinidad  asphalt  and  the 
maltha  in  the  proportion  of  100  to  80,  which  had  a  penetration  of 
65°.  This  cement  was  then  maintained  for  9  hours  at  a  tempera- 
ture of  325°  F.,  when  it  was  found  to  have  hardened  so  much  as  to 
penetrate  but  24°. 

Of  course  satisfactory  surface  mixtures  for  paving  cannot  be 
made  with  such  changeable  material,  and  this  is  the  reason  that 
much  of  the  earlier  work  done  with  California  asphalt  was  a  fail- 
ure. 

In  fact,  slight  reflection  shows  that  for  a  fluxing  agent  for 
softening  hard  asphalt  a  substance  is  needed  which  does  not 
change  its  consistency  after  prolonged  heating,  and  not 
another,  though  perhaps  softer  asphalt,  which  gradually 
becomes  converted  into  a  hard  asphalt  under  the  influence 
of  heat. 

Asphalt  Cements  Composed  of  other  Solid  Native  Bitumens 
than  Ordinary  Asphalts  and  Asphaltic  Fluxes. — Entirely  satis- 
factory cements  for  use  in  the  paving  industry  have  been  made 
from  some  of  the  other  native  bitumens,  especially  Gilsonite, 
by  fluxing  them  with  an  asphaltic  oil.  For  this  purpose  about 
equal  parts  of  the  Gilsonite  and  flux  are  necessary.  The  resulting 
cement  contains  bitumen  in  the  form  of  the  classes  known  as 
malthenes  and  asphaltenes  in  normal  proportions,  about  the 
same  as  in  Trinidad  and  Bermudez  asphalt  cements,  as  will  appear 
from  data  on  page  308.  On  this  account,  such  cements  may  be 
regarded  as  entirely  normal  in  character,  and  the  fact  that  they 
contain  a  large  proportion  of  flux  is  not  open  to  comment,  espe- 
cially as  the  hard  bitumen  and  the  oils  combine  homogeneously 
and  no  free  flux  is  found  in  the  cement. 


REFINING    OF    SOLID    BITUMENS.  307 

Asphalt  Cements  Composed  of  Solid  Residual  Bitumens  from 
Asphaltic  Petroleum  Brought  to  a  Proper  Consistency  with 
Residuum  of  the  Same  Origin. — From  the  asphaltic  petroleums, 
such  as  those  found  in  California  and  Texas,  residual  pitches  or 
solid  bitumens  are  prepared  by  distillation,  and  the  charac- 
teristics of  these  solid  bitumens  have  been  already  described. 
Asphalt  cements  can  be  prepared  for  paving  purposes  from  these 
residual  pitches  by  bringing  them  to  a  proper  consistency  with 
a  residuum  or  flux  made  from  the  same  petroleum.  These  cements 
have  been  used  with  some  success  and  also  with  many  resulting 
failures.  They  are  very  susceptible  to  temperature  changes, 
which  necessitates  the  use  of  a  very  carefully  graded  mineral 
matter  with  plenty  of  filler  and  the  greatest  skill  hi  handling 
them  in  order  that  they  may  not  harden  while  being  mixed  with 
hot  sand  or  reach  the  street  at  such  a  degree  of  softness  that  they 
mark  up  very  rapidly  under  hot  summer  suns. 

Cements  of  this  description  have  been  used  to  a  very  consider- 
able extent  on  the  Pacific  Coast,  and  they  are  quite  suitable  for 
the  climate  of  Southern  California.  In  Washington  and  Oregon 
some  difficulties  have  been  met  with  where  they  have  been  employed. 

Asphalt  Cements  of  Any  of  the  Previous  Classes  to  which* 
Amendments  of  Residual  Pitches  or  Blown  Oils  Have  Been  Added. — 
Excellent  asphalt  cements  have  been  prepared  for  paving  purposes 
to  which  additions,  not  exceeding  10  per  cent  in  amount,  of  con- 
densed or  blown  oils,  such  as  Pittsburg  flux,  Ventura  flux,  or  blown 
Beaumont  oil  have  been  made.  While  tiie  materials  constituting 
these  additions  are  in  themselves  unsuitable  for  paving  purposes, 
they  seem  in  some  instances  to  modify  the  properties  of  native 
bitumen  in  such  a  way  as  to  improve  them,  although  in  a  manner 
that  cannot  be  described.  Such  cements  are  not  to  be  objected 
to,  since  they  have  been  shown  by  experience  to  give  satisfactory 
results. 

Characteristics  of  Asphalt  Cement. — It  is  of  interest  to  note 
the  characteristics  of  asphalt  cement  prepared  from  various  bitu- 
mens with  various  proportions  of  fluxes,  especially  as  to  the  rela- 
tive proportions  of  the  malthenes  and  asphaltenes  which  they 


308 


THE  MODERN  ASPHALT  PAVEMENT. 


contain.     Some  data  in  regard  to  this  are  given  in  the  following 
table: 


Asphalt. 

Flux. 

Proportions. 

1 
1 

Bitumen  by  CSj. 

Mineral  Matter. 

Difference. 

V 

Per  Cent  Total. 

Fixed  Carbon. 

Trin.  Lake  . 

Texas 

100-19.0 

40 

64.2 

31.0 

4.8 

46.7 

72.7 

8.3 

asphal- 

100-25.0 

60 

67.6 

28.3 

4.1 

50.2 

74.3 

8.2 

tic 

100-33.3 

80 

70.0 

25.9 

4.1 

52.2 

74.6 

7.6 

Trin.  Lake  . 

Paraf- 

100-19.5 

40 

64.7 

30.5 

4.8 

46.0 

71.1 

8.9 

fine 

100-23.5 

60 

66.1 

29.2 

4.7 

47.2 

72.6 

8.8 

100-26.6 

80 

67.5 

27.7 

4.8 

48.6 

72.0 

8.1 

Trin.  Land 

Paraf- 

100-17.6 

40 

63.1 

30.9 

6.0 

44.3 

72.0 

9.2 

fine 

100-25.0 

60 

64.3 

29.6 

6.1 

47.3 

73.5 

9.8 

100-28.2 

80 

65.5 

28.8 

5.7 

49.0 

74.8 

9.0 

Berm.  Lake. 

Texas 

100-  5.3 

40 

94.8 

2.4 

2.8 

69.0 

72.8 

13.0 

asphal- 

100-14.9 

60 

95.2 

2.4 

2.4 

71.6 

75.1 

12.1 

tic 

100-22.0 

80 

95.0 

2.1 

2.9 

72.2 

76.0 

11.6 

Berm.  Lake. 

Paraf- 

100-  5.3 

40 

94.2 

2.2 

3.6 

68.0 

72.2 

12.7 

fine 

100-14.9 

60 

95.5 

2.0 

2.5 

71.0 

74.3 

12.4 

k 

100-22.0 

80 

95.4 

2.2 

2.4 

71.3 

74.7 

12.2 

Gilsonite  .  .  . 

Texas 

100-85.2 

60 

99.7 

.2 

.1 

76.3 

77.1 

8.1 

asphal- 

tic 

100-96.1 

80 

99.8 

.1 

.1 

76.8 

77.6 

7.7 

D  grade,  Cal. 

G  grade 

100-12.4 

80 

99.7 

.2 

.1 

70.8 

71.5 

16.0 

Texas  resid- 

Texas 

100-20.4 

40 

98.6 

.2 

1.2 

70.5 

71.5 

19.1 

ual  pitch 

asphal- 

100-25.0 

60 

98.9 

.2 

.9 

71.9 

72.7 

18.3 

tic 

100-33.3 

80 

98.8 

.1 

1.1 

73.8 

74.7 

17.2 

Cuban  Beju- 

Texas 

100-49.0 

40 

68.3 

26.1 

5.6 

48.8 

71.4 

11.9 

cal 

asphal- 

100-50.0 

60 

70.0 

23.5 

6.5 

50.7 

72.4 

11.1 

tic 

100-55.0 

80 

76.0 

18.1 

5.9 

56.0 

73.7 

11.0 

Grahamite.  . 

Texas 

100-150.0 

40 

99.5 

.1 

.4 

63.3 

63.6 

9.8 

asphal- 

100-203.0 

60 

99.5 

.1 

.4 

70.4 

70.7 

8.4 

tic 

100-233.3 

80 

99.5 

.1 

.4 

71.3 

71.6 

8.1 

Physical  Properties  of  Asphalt  Cement. — The  character  of 
a  sheet  asphalt  surface  of  ordinary  type  will  depend  very  largely 
on  the  properties  of  the  cementing  material  which  binds  the  mineral 
aggregate  together,  even  if  the  latter  is  of  the  most  approved 


REFINING    OF   SOLID    BITUMENS.  309 

grading  and  consequent  stability.  When  the  latter  is  not  careiolly 
arranged  the  physical  properties  of  the  asphalt  cement  will  have 
an  even  greater  influence  on  the  behavior  of  the  asphalt  surface, 
more  particularly  under  great  extremes  of  temperature.  It  is 
important,  therefore,  to  examine  the  properties  of  asphalt  cements 
prepared  from  different  solid  native  bitumens  and  softened  with 
various  fluxes.  The  properties  which  are  of  the  greatest  impor- 
tance have  been  generally  accepted  to  be  their  greater  or  smaller 
susceptibility  to  changes  in  consistency  at  the  extreme  temperatures 
which  they  meet  under  different  climatic  conditions  and  to  their 
variable  ductility. 

The  fact  that  asphalt  cements  vary  in  consistency,  with  change 
of  temperature,  means  that  at  certain  temperatures  they  are  very 
viscous  liquids  and  at  low  temperatures  slightly  viscous  solids,  the 
transition  from  one  state  to  another  being  very  gradual,  although 
under  modern  theories  of  physical  chemistry  substances  which  are 
not  crystalline  can  hardly  be  regarded  as  being  solids.  The  slow 
flow  of  crude  Trinidad  asphalt,  where  large  heaps  of  it  are  stored, 
is  a  well-known  occurrence  arfd  corresponds  very  closely  to  that 
of  the  glacial  flow  of  ice.  The  flow  of  an  asphalt  cement  con- 
taining a  very  considerable  proportion  of  flux  is,  of  course,  much 
more  rapid.  Mr.  A.  W.  Dow1  has  shown  that  when  cubes  of  asphalt 
cement  are  placed  over  a  hole  in  a  board  at  temperatures  of  26°  F., 
75°  F.  and  140°  F.,  the  movement  of  the  material  into  the  hole 
was  visible  in  1  hour  at  140°  F.,  in  a  longer  time  at  75°  F.,  and  in 
I  week  at  the  lowest  temperature.  The  fact  that  an  asphalt  cement 
will  flow  at  this  low  temperature  is  of  great  importance  in  connec- 
tion with  the  behavior  of  asphalt  surface  on  the  street  in  the  winter 
months.  Unless  there  is  some  ductility  to  allow  for  the  contraction 
in  the  mass  of  the  mineral  aggregate  all  asphalt  surfaces  would 
crack  at  such  a  season.  That  they  do  not  do  so  in  all  cases  is  to 
be  attributed  to  this  and  to  the  fact  that  a  suitable  asphalt  cement 
possesses  such  a  consistency  and  lack  of  susceptibility  to  change 
*n  this  respect  between  the  lowest  and  the  highest  temperature 
to  which  it  is  exposed  as  to  prevent  it.  Cracking  frequently  does 

1  Municipal  Engineering,  1898,  15,  364. 


310  THE    MODERN    ASPHALT    PAVEMENT. 

take  place  in  asphalt  pavements  from  the  lack  of  such  qualities 
in  the  asphalt  cement  of  which  they  are  composed  or  from  the 
absence  of  a  sufficient  amount  of  it  as  will  appear  in  the  discussion 
in  later  pages  on  the  defects  in  asphalt  pavements,1  but  is  oftener 
due  to  the  hardness  of  a  cement  rather  than  to  its  lack  of  ductility 
as  experiments  have  shown  that  some  asphalt  cements,  if  suffi- 
ciently soft,  although  very  short,  may  be  sufficiently  ductile  to 
meet  the  demands  made  upon  them  at  low  temperature. 

Experiments  have  shown  that  the  ductility  of  an  asphalt 
cement  is  proportionate  to  the  amount  of  flux  which  it  contains 
rather  than  to  the  character  of  the  same  and  as  the  result  of  a 
very  extended  investigation,  the  results  of  which  are  too  lengthy 
and  numerous  to  introduce  here,  it  has  been  made  evident  that 
too  much  dependence  cannot  be  placed  upon  this  characteristic 
in  forming  an  opinion  as  to  the  availability  of  an  asphalt  for  paving 
purposes. 

The  susceptibility  of  asphalt  cements  to  changes  in  consistency 
with  change  in  the  temperature  of  its  environment  can  be  shown 
in  several  ways,  most  conveniently  by  determining  the  consistency 
at  different  temperatures  with  one  of  the  various  penetration 
machines  in  use  for  this  purpose,  by  the  relative  elongation  of 
cylinders  of  different  cements  under  tension  at  different  tempera- 
tures or,  in  the  case  of  high  temperatures,  by  the  length  of  flow 
of  small  cylinders  of  cement  on  a  corrugated  brass  plate  in  the 
manner  described  in  Chapter  XXVIII.  If  asphalt  cements  are 
prepared  from  different  asphalts  and  fluxes  of  such  a  consistency 
that  they  all  have  the  same  penetration  at  the  normal  tempera- 
ture, 78°  F.,  and  are  then  again  penetrated  at  extremely  low 
and  high  temperatures  the  relative  changes  in  the  consistency 
can  then  be  determined,  as  has  been  already  shown.2 

In  the  following  table  are  presented  the  results  of  the  deter- 
mination of  the  consistency  of  the  asphalt  cement  made  from 
various  asphalts  with  fluxes  of  different  character  at  41°  F.  and 
100°  F.  all  the  cements  having  the  same  consistency  at  78°  F. 

Although  the  results  speak  for  themselves  it  may  be  well  to 

1  See  page  480-2.  2  See  page  301. 


REFINING    OF    SOLID    BITUMENS. 
THE  MODERN  ASPHALT  PAVEMENT. 


311 


Asphalt. 

Flux. 

Parts 
Flux  to 
100  of 

Asphalt. 

Pen. 
Bowen, 

78°  F. 

Penetrometer. 

41°  F.i 

78°  F.i 

100°  F.i 

Trinidad  Lake  

1  1            1  1 

it            ft 
Bermudez  

Heavy 

25 
34 
22 

17.5 
24 
15 

65 
65 
65 

65 
65 
65 

65 

65 
65 
65 

65 
65 

3 

2 

5 

5 
3 
3 

3 

5 
5 

7 

6 
5 

41 
42 
32 

44 
40 
39 

43 

34 
37 
30 

28 
22 

97 
113 
91 

100 
109 
108 

98 

63 

82 
48 

35 
37 

Extra  Heavy  .  .  . 
Paraffine  

Heavy 

1  1 

Extra  Heavy  .  .  . 
Paraffine  

None 

Gilsonite  .  .  . 

He  aw 

127 
170 
122 

270 

51 

it 

Extra  Heavy  .  .  . 
Paraffine 

ft 

Grahamite    . 

Extra  Heavy  .  .  . 
Heavy  .  . 

Cuban  Bejucal  

1  41°  F.  =  200  grams,  5  seconds;  78°  F.  =  100  grams,  5  seconds;  100°  F.= 
50  grams,  5  seconds. 

call  attention  to  some  of  the  facts  that  are  brought  out  by  them. 
Among  the  Trinidad  cements  that  made  with  extra  heavy  oily 
and  consequently  requiring  the  largest  proportion  of  flux,  is 
much  more  susceptible  to  high  temperatures,  having  a  penetra- 
tion at  100°  F.  of  113°,  while  that  made  with  the  paraffine  oil, 
of  which  only  22  pounds  per  100  was  employed,  has  a  penetra- 
tion of  only  91°,  while  all  the  Trinidad  cements  had  practically 
the  same  penetration  at  41°  F. 

Asphalt  cements  made  with  gilsonite  and  grahamite  are  much 
less  susceptible  to  changes  in  consistency  at  extreme  tempera- 
tures. At  41°  F.  cements  made  from  these  materials,  although 
having  the  same  penetration  as  the  Trinidad,  Bermudez,  and 
California  cements  at  78°  F.,  are  much  less  hard  and  in  the  same 
way  are  softer  to  a  less  degree  at  higher  temperatures.  This 
would  show  that  such  cements  would  be  more  satisfactory  for  use 
in  the  paving  industry  where  extremes  of  temperature  are  to  be 
met  than  those  composed  of  true  asphalts. 


312  THE    MODERN   ASPHALT    PAVEMENT. 

SUMMARY. 

In  the  preceding  chapter  the  technology  of  the  paving  indus- 
try has  been  discussed  in  detail  from  the  refining  of  the  native 
bitumen  to  the  preparation  of  the  asphalt  cement,  together  with 
a  study  of  the  character  of  the  various  asphalt  cements  made 
from  different  solid  bitumens  and  with  different  fluxes.  This 
chapter  in  its  detail  will  interest  principally  the  asphalt  expert, 
the  engineer,  and  the  specialist. 


CHAPTER  XVI. 
SURFACE  MIXTURES. 

THE  surface  mixtures  of  the  early  days  of  the  asphalt  paving 
industry  consisted,  as  they  do  to-day,  of  asphalt  cement,  ground 
limestone,  and  sand;  but  even  in  1893  very  little  attempt  was  made 
to  specify  fhe  character  of  these  consituents  or  to  determine  what 
rdles  they  play  in  the  finished  pavement.  The  asphalt  cement  was 
at  one  time  soft,  at  another  hard,  at  one  time  too  small  in  amount 
and  again  too  large,  but  oftener  too  small;  the  ground  limestone 
was  expected  in  1884  to  be  only  so  fine  that  16  per  cent  should  be 
an  impalpable  fine  powder  and  all  should  pass  a  No.  26  mesh, 
hardly  what  would  be  considered  a  dust  to-day,  and  at  times  it 
was  held  to  be  doubtful  if  there  were  any  necessity  for  the  use 
of  dust  at  all.  The  sand  was  sometimes  coarse  and  sometimes 
fine,  depending  on  the  most  available  local  supplies,  and  only  in 
the  later  years  were  two  kinds  mixed  and  that  without  much 
reasoning. 

In  1884  it  was  specified  that  the  sand  in  use  in  Washington  should 
all  pass  a  20-mesh  sieve  and  none  of  it  an  80. 1 

Surfaces  with  coarse  sand  and  much  cement  marked  or  pushed 
and  then  the  bitumen  was  reduced;  with  fine  sand  and  low  bitumen 
they  cracked  and  the  other  extreme  was  again  sought.  Every- 
thing was  done  by  rule  of  thumb  and  without  reason.  To  this 
state  of  affairs  much,  but  not  all,  of  the  cracking,  displacement, 
and  defects  in  pavements  laid  in  the  early  nineties  was  due.  The 
average  consistency  of  the  cement  was  the  same  for  years  and  was 

1  Annual  Report  of  the  Operations  of  the  Engineer  Dept.,  District  of 
Columbia,  for  the  year  ending  June  30,  1884,  101. 

313 


314 


THE  MODERN  ASPHALT  PAVEMENT. 


too  hard  in  most  cases  because  the  defective  mineral  aggregate 
would  not  permit  the  use  of  a  softer  one.  The  limestone  dust  was 
most  of  it  sand  and  in  consequence  the  amount  of  filler  in  the  mix- 
ture was  very  deficient.  But,  worst  of  all,  the  sand  grading  was 
arranged  by  chance.  Specimens  of  old  surfaces  were  collected 
in  1894  and  studied  by  the  author  at  the  request  of  the  President 
of  the  Barber  Asphalt  Paving  Company  as  being  representative 
of  the  best  work  of  the  company  up  to  that  time,  although  they, 
on  this  account,  hardly  illustrate  the  average  pavement  of  that  day. 
They  were  analyzed  in  Washington  and  showed  the  following 
variations  in  their  mineral  aggregate,  filler,  and  bitumen.  Among 
these  variations  those  in  the  sand  grading  are  most  striking. 

AVERAGE  COMPOSITION  OF  SURFACES  FROM  VARIOUS  CITIES, 
LAID  BEFORE  1894,  ARRANGED  ACCORDING  TO  THE  PER- 
CENTAGES  OF  100-  AND  80-MESH  SAND  THEY  CONTAIN. 


aty. 

Bitumen. 

Mineral  Aggregate  Passing  Mesh 

Total. 

200. 

100  and  80 

50  and  40. 

30,20,  and 
10. 

Washington  

10.29 
8.91 
8.81 
9.61 
9.06 
9.87 
10.97 
10.64 
11.75 
9.85 
10.32 
9.65 
9.24 
9.44 

9.89 
10.5 

9.72 
14.50 
8.38 
10.87 
10.93 
11.27 
12.13 
12.15 
14.46 
13.10 
11.91 
11.32 
9.33 
12.80 

11.63 
13.0 

6.45 
9.06 
9.48 
12.12 
12.77 
15.34 
16.39 
22.01 
35.32 
25.92 
29.19 
30.53 
35.95 
41.98 

21.61 
26.0 

42.06 
38.30 
41.26 
60.10 
49.06 
52.59 
34.14 
37.58 
26.19 
31.31 
39.38 
44.68 
38.83 
24.93 

40.03 
34.5 

31.48 
29.23 
32.07 
7.30 
18.18 
10.93 
26.37 
17.62 
12.28 
19.82 
9.20 
3.82 
6.65 
10.85 

16.84 
16.0 

=  100% 
=  100% 
=  100% 
=  100% 
=  100% 
=  100% 
=  100% 
=  100% 
=  100% 
=  100% 
=  100% 
=  100% 
=  100% 
=  100% 

=  100% 
=  100% 

Louisville  

Newark 

St  Louis 

Youngstown  
New  Orleans  
New  York  
Scranton     

Boston         

Kansas  City  

Schenectady  

Buffalo 

Chicago 

Omaha 

Average  

FOR   COMPARISON. 

Standard  mixture.  .  . 

These  surfaces  present  every  variety  of  grading  in  their  com- 
position and  it  is  apparent  that  they  could  not  all  be  satisfactory. 
Evidently  no  system  was  carried  out  in  their  production.  The 
percentage  of  bitumen  varies  from  8.8  to  11.7,  probably  not  from 


SURFACE   MIXTURES.  315 

carelessness  entirely  but  because  the  mineral  aggregate  would 
permit  of  the  use  of  a  large  amount  in  certain  cases  and  less  in  others. 
The  amount  of  filler  or  200-mesh  dust  is  deficient  in  many  cases, 
although  in  some  it  seems  high  enough,  owing  to  the  presence  of 
sand  of  200-mesh  size  which,  as  will  appear,  does  not  act  as  filler. 

As  will  be  shown  later,  the  amount  of  100-  and  80-mesh  material 
is  deficient  in  the  first  seven  cities  and  unbalanced  in  all.  The 
grains  of  10-,  20-,  and  30-mesh  sizes  are  present  in  far  too  large  a 
degree  in  Washington,  Louisvile,  Newark,  and  New  York,  and  are 
not  well  regulated  in  most  of  the  cities.  In  fact  the  mineral  aggre- 
gate in  none  of  these  towns  was,  at  that  time,  well  graded. 

If  the  records  of  the  Barber  Asphalt  Paving  Company  are 
studied  for  the  10  years  before  1899,  as  summarized  in  the  following 
tables,  the  reason  for  the  varied  composition  of  the  preceding 
mixtures  is  explained.  All  sorts  of  sands  were  used,  and  probably, 
although  there  are  no  records,  all  kinds  of  filler.  See  results  tabu- 
lated on  pages  316,  317,  318,  and  319. 

If  the  average  grading  of  the  sand  and  of  the  mineral  aggregates 
of  these  same  cities  be  examined  as  far  as  the  incomplete  data  will 
admit,  the  peculiarities  of  this  part  of  the  surface  mixture  are 
apparent.  As  fine  sieves  were  not  in  use  in  the  early  days  of  the 
industry  our  knowledge  of  the  grading  of  the  finer  part  of  the 
aggregate  is  limited,  but  in  the  sands  of  1889  it  is  readily  seen  that 
in  that  used  in  Chicago  there  were  not  enough  coarse  particles, 
while  the  Newark  and  New  York  sands  were  only  fit  for  concrete. 
Buffalo  was  deficient  in  80-  and  100-mesh  particles,  as  were  Kansas 
City,  Louisville,  and  Washington.  Other  defects  were  apparent 
in  this  and  the  following  years,  to  which  it  is  unnecessary  to  call 
attention  here,  as  the  data  are  open  to  examination  in  the  tables 
and  the  most  striking  points  have  been  marked  with  asterisks. 
In  1893,  for  instance,  all  the  sands  were  much  too  coarse  except 
in  Buffalo  and  Chicago.  In  1894  they  were  much  better.  It  is 
sufficient  to  say  that  up  to  1894  no  effort  based  on  any  well-defined 
reasons  had  been  made  to  regulate  the  grading  of  the  sand  in 
surface  mixtures  or  to  accommodate  the  dust  and  asphalt  cement 
to  the  demands  of  the  latter,  although  it  had  been  determined  in 
1892  that  in  the  better  class  of  pavements  the  sand  was  fine. 


316 


THE  MODERN  ASPHAL1  PAVEMENT . 


AVERAGE  SANDS. 

1889. 


City. 

Passing 

Ret.  10 

70 

50 

40 

30 

20 

10 

Boston  

8* 
29 
20* 
12* 
6* 

10 
41 

28 
9* 

50 
49 
22 
43 
10 

15 
33 

31 
10* 

26 
16 
18 
22 
11 

15 
10 

17 
24 

11 
5 
20 
12 
17 

20 

8 

10 

sot 

3* 
1* 

tit 

5 
23 

18 
3 

7 
19f 

1* 
0* 
7 
3 
27 

18 
2 

6 
6 

0 
0 
1 
1 
6 

4 
1 

1 
3 

Buffalo  1-B 

Chicago               

Kansas  City  

Louisville  

Newark  

New  Orleans  

New  York 

Omaha              

St  Louis     

Scranton  

Washington  

1891. 


Passing 

200 

70 

50 

40 

30 

20 

10 

Boston     

5 

38 

19 

11 

10 

10 

8f 

o 

Buffalo  1-B  

9 

45 

32 

6 

3* 

1* 

2* 

1 

Chicago 

4 

11 

24 

21 

18 

12 

9 

1 

Kansas  City  
Louisville 

3 

21 

18 

14 

17 

14f 

12f 

1 

Newark 

4 

9* 

11 

10 

18 

23t 

23t 

3 

New  Orleans  
New  York  

4 

23 

21 

16 

16 

10 

9 

2 

Omaha  
St  Louis           • 

3 

16* 

20 

18 

27 

11 

5 

Scranton 

5 

23 

16 

16 

14 

16t 

lit 

o 

Washington  

4 

3* 

13* 

26 

29t 

16t 

7 

1 

*  Too  low. 


t  Too  high. 


SURFACE    MIXTURES. 


317 


MINERAL  AGGREGATE. 
1892 


rs*» 

Passing 

Ret  10 

City. 

200 

70 

50 

40 

30 

20 

10 

Boston           

18 

21 

11 

14 

14 

16f 

6 

1 

Buffalo  1-B  

13 

53 

16 

9 

3 

3 

3 

3 

Chicago      

12 

29 

27 

16 

9 

6 

3 

0 

Kansas  City  
Louisville  
Newark  
New  Orleans  
New  York  

7 
12 
7 
6 
12 

6* 
21 
11* 
0* 
21 

7 
20 
17 
11 
13 

13 
25 
22 
39 
14 

20 
13 
20 
32 
15 

28f 
6 
18 
11 
15 

18t 
3 
6 
2 
10 

3 
0 

1 
1 
3 

Omaha 

6 

17 

10 

13 

15 

21  1 

17f 

2 

St.  Louis  
Scranton  

7 

13* 

6 

13 

22 

29f 

12f 

0 

Washington  

9 

6 

8 

30 

33 

12 

2 

0 

1893. 


Boston 

22 

16 

17 

22f 

20f 

5 

Buffalo        

51  f 

27 

12 

5 

3 

2 

Chicago      

47 

26 

14 

7 

3 

3 

Kansas  City  
Louisville  
Newark 



41 
16* 

16 
12 

13 
17 

11 

18 

10 
23 

lot 

14 

New  Orleans  
New  York  

24 

10 

14 

19 

19t 

14f 

Omaha 

31 

17 

13 

14 

14f 

lit 

St  Louis 

28 

14 

15 

17 

17f 

9 

Scranton      

Washington  

20* 

13 

23 

26 

13f 

6 

1894. 


Pitv 

Passing 

Ret  10 

City. 

100 

70 

50 

40 

30 

20 

10 

Boston  

16 

22 

25 

15 

14 

8 

2 

Buffalo 

17 

30 

34 

12 

4 

2 

2 

Chicago  
Kansas  City  
Louisville  

15 
29 

19 
21 

33 
24 

14 
9 

7 
7 

5 
5 

5 
5 

Newark  
New  Orleans  
New  York  

15 

8* 

19 

13 

14 

14t 

14t 

Omaha  

21 

28 

23 

10 

8 

6 

St  Louis 

Scranton 

18 

15 

27 

14 

9 

8 

11 

Washington  

11 

5* 

12 

20 

31t 

17t 

5 

*  Too  low. 


t  Too  high. 


318 


THE    MODERN    ASPHALT    PAVEMENT. 


MINERAL  AGGREGATE. 

1895. 


Passing 

City. 

100 

70 

50 

40 

30 

20 

10 

Ret.  10 

Boston  

24 

17 

21 

14 

11 

8 

7 

Buffalo  

18 

32 

30 

9 

3 

4 

5 

Chicago  
Kansas  City 

22 
27 

19 
19 

26 

24 

12 

10 

6 

7 

6 

8 

9 
5 

Louisville    

17 

16 

33 

14 

9 

6 

4 

Newark  

16 

12* 

17 

14 

14 

14f 

14t 

New  Orleans  
New  York 

18 
21 

14* 
15* 

25 
15 

19 
12 

13 
13 

8 

2 

Omaha 

21 

22 

21 

11 

9 

6 

7 

St  Louis   

Scranton  

19 

12* 

21 

17 

13 

11 

8 

Washington  

1896. 


City. 

Passing 

200 

100 

80 

50 

40 

30 

20 

10 

Boston 

12.1 
7.4 

9.9 
13.7 
12.2 
11.2 
11.6 
14.4 
10.6 
15.9 
11.0 
8.7 

14.4 
6.2 
13.7 
8.7 
5.4* 
8.9* 
9.4* 
11.6 
11.9 
10.4 
9.5* 
6.7* 

14.3 
20.1 
18.8 
17.5 
12.6 
10.2 
11.3 
11.9 
20.3 
14.6 
12.3 
10.4 

27.0 
49.3 
31.1 
40.6 
53.8 
25.0 
31.6 
25.5 
33.8 
36.6 
29.1 
31.2 

11.0 
8.1 
9.2 
6.7 
8.1 
14.8 
14.7 
13.3 
9.2 
11.4 
15.0 
20.1 

9.2 
3.8 
6.5 
5.3 
3.7 
12.9 
12.5 
10.6 
6.5 
6.8 
12.3 
14.7 

6.0 
2.1 
5.2 
3.6 
2.0 
8.4 
6.0 
6.5 
4.1 
4.9 
6.6 
5.4 

6.0 
3.0 
5.6 
3.9 
2.1 
8.6 
3.0 
6.2 
3.5 
1.2 
4.2 
2.8 

Buffalo  1-B.  ..... 
Chicago  Pit.  1.  ... 
Kansas  City  
Louisville  

Newark  

New  Orleans  
New  York 

Omaha 

St.  Louis  
Scranton  

Washington  

1897. 


Boston  

16.5 

14.9 

12.5 

26.6 

10.1 

8.5 

5  2 

5  7 

Buffalo  1-B 

15  3 

12  6 

16  3 

46  3 

5  7 

2  5* 

0  8* 

0  5* 

Chicago 

15  7 

16  4 

19  5 

36  3 

5  0 

2  7* 

2*7 

1  7 

Kansas  City 

21   1 

14.6 

15  3 

34.5 

5.1 

3  6 

2  9 

2  7 

Louisville  
Newark          

14.9 
17.3 

6.4* 
12.2 

10.5 
9.8* 

54.4 
27.3 

7.5 
10.5 

3.2 
10.9 

1.8 
7  2 

1.2 

4  8 

New  Orleans  
New  York  

14.1 
18.4 

11.1 
14.5 

9.9* 
13.9 

28.9 
27.7 

13.3 
9.4 

11.6 
8.0 

6.6 
4.6 

4.5 
3  5 

Omaha 

14  6 

14  0 

17  5 

35  5 

7  4 

5  6 

2  9 

2  5 

St  Louis   .  . 

23  2 

12  7 

18  2 

32.1 

6.7 

3  8 

2  0 

1  2 

Scranton  

13.7 

9.0 

11.5 

31.1 

12.3 

11.8 

5  9 

4  6 

Washington  

11.4 

8.4 

7.5 

27.1 

17.2 

13.4 

9.5f 

5.4 

*  Too  low. 


t  Too  high. 


SURFACE    MIXTURES. 


319 


MINERAL  AGGREGATE. 
1898. 


City. 

Passing 

200 

100 

80 

50 

40 

30 

20 

10 

16.4 
15.8 
14.6 
16.2 
16.7 
12.9 
12.3 
15.3 
13.0 
14.9 
13.8 
13.8 

15.2 
14.3 
17.3 
13.6 
11.8 
12.5 
8.7* 
14.6 
15.6 
10.9 
12.0 
9.3 

14.3 
19.2 
14.8 
15.6 
11.3 
8.4* 
11.1 
15.0 
19.2 
16.6 
11.7 
8.6 

28.3 
40.1 
37.6 
31.9 
34.3 
20.6 
34.6 
25.3 
32.9 
41.9 
29.7 
29.1 

11.0 
6.1 
9.4 
8.3 
10.9 
14.4 
15.8 
11.2 
8.0 
6.4 
13.2 
20.0 

7.5 
2.8* 
3.4* 
6.5 
7.3 
12.0 
11.1 
8.5 
5.3 
4.3 
9.9 
10.7 

4.4 
1.6 
2.1 
4.5 
3.8 
11.6 
4.1 
6.3 
3.6 
3.0 
5.6 
5.2 

2.9 
0.1 
0.7 
3.1 
4.0 
7.6 
2.3 
3.9 
2.4 
1.9 
3.9 
3.2 

Buffalo  1-B  

Chicago      

Kansas  City  

Louisville  

Newark 

New  Orleans 

New  York 

Omaha           .... 

St  Louis   

Scranton  

Washington 

1899. 


Boston  

16.2 

13.6 

10.4 

24.9 

15.7 

8.4 

6.4 

4.4 

Buffalo  1-B  
Chicago  
Kansas  City  
Louisville  

14.7 
12.9 
13  5 
17.4 

11.8 
16.0 
10.3 
8.0* 

18.7 
17.3 
15.5 
5.1* 

41.6 
38.5 
43.9 
41.3 

7.0 
8.5 
7.9 
21.6 

2.8* 
3.1* 
4.0* 
3.4* 

1.9 
2.0 
3.0 
2.0 

1.5 
1.6 
1.9 
1.2 

Newark  
New  Orleans 

16.2 
14  0 

15.2 
12  4 

10.7 
10  4 

12.9 
28  4 

12.5 
19  0 

10.8 
7  7 

11.7 
5  7 

9.9 
2  4 

New  York  

14  5 

14  2 

14  1 

26.7 

13  5 

7  4 

5  9 

3  7 

Omaha  

14  8 

14.7 

13.9 

28.6 

12.9 

6.3 

5.2 

3.6 

St.  Louis  

13.8 

13.7 

12.3 

33.2 

12.7 

6.0 

4.8 

3.5 

Scranton  

14.5 

12.9 

12.2 

25.6 

16.7 

8.6 

5.8 

3.7 

Washington  

14.2 

8.5* 

5.8* 

19.5 

22.4 

11.2 

9.8 

8.5f 

'Too  low. 


t  Too  high. 


Bitumen  in  the  Surface  Mixtures  of  the  Earlier  Days  of  the 
Industry. — Up  to  1896  the  bitumen  in  surface  mixtures  was  very 
variable  in  amount,  and,  as  a  rule,  too  low,  owing  probably  to 
the  necessity  of  keeping  it  at  such  a  point  because  of  the  poor 
sand  grading  and  the  absence  of  binder,  to  avoid  displacement 
of  the  street  surfaces.  The  following  tables  show  the  average 
and  extreme  per  cents  of  bitumen  in  the  surfaces  laid  by  the  Bar- 
ber Asphalt  Paving  Company  in  a  number  of  cities  during  the 
earlier  years  of  which  records  are  available. 


320 


THE  MODERN  ASPHALT  PAVEMENT. 


AVERAGE  AND  EXTREME  PERCENTAGES  OF  BITUMEN  IN 
SURFACES  OF  THE  BARBER  ASPHALT  PAVING  COMPANY 
FOR  ELEVEN  YEARS,  1889-1899. 


City. 

1889 

1890 

1891 

1892 

1893 

Boston     

9.3-10.9 

8.9-14.5 

8.6-12.0 

9  3-10  3 

Buffalo  

10.0 
8.4-12.2 

7.6^i2.2 

11.1 
8.1-12.5 

10.2 
7.2-15.9 

9.8 
8.1-13.7 

Chicago 

9.8 
8  6-10  5 

10.2 
9  0-11  5 

10.0 
7  9-11  7 

10.1 
8  8-11.5 

10.3 
9  2-11.7 

Kansas  City  

9.8 
8.0-12.3 

10.1 
8.0-11.1 

9.5 

7.7-11.7 

10.1 
8.9-12.3 

10.3 
9.0-11.3 

Louisville  

9.9 
10.4-11.5 

9.3 
7.8-10.7 

10.2 
10.1-12.1 

10.3 
8.9-10.8 

10.2 

Newark  

10.7 
6.7-10.7 

9.3 

10.9 
6.9-13.0 

9.6 
7.8-10.9 

9.2-10.2 

New  Orleans.  •  

9.0 
8.1-10.6 



9.6 

9.8 
8.8-10.4 

9.7 

9.2 

9.5 

New  York       

8.4-12.9 

8  6-12.7 

7  9-13.1 

8.3-11.7 

8.9-13.4 

10.8 
8.5-11.0 

10.8 
8.6-12.4 

10.6 
8.0-11.6 

10.1 
7.7-11.5 

10.5 

8.8-9.8 

St  Louis 

9.8 
9.6-11.2 

10.2 

9.8 

9.4 
9  6-12.8 

9.4 
7  3-11.7 

10.1 

9.7 

9.7 

8.5-11.2 

8.8-11.6 

8.2-14.2 

9.2-12.2 

Washington  

10.1 

8.8-15.5 

10.6 
9.1-11.4 

10.5 
8.7-11.5 

10.6 

8.8-12.8 

9.6-10.9 

Averaee.  . 

9.8 
9.9 

10.2 
10.1 

10.3 
10.2 

10.7 
10.0 

10.2 
10.0 

City. 

1894 

1895 

1896 

1897 

1898 

1899 

Boston  

8.4-10.0 
9.4 
6.9-11.9 
10.0 
8.2-11.7 
9.8 
8.0-12.1 
9.9 

7.5-11.1 
9.9 
8.3-10.6 
9.4 
8.4-11.0 
9.9 
8.3-10.7 
9.3 
8.0-11.6 
10.0 
7.8-10.6 
9.3 
9.1-10.9 
10.0 
7.9-11.3 
9.9 
7.4-10.9 
9.1 

8.7-11.1 
9.9 
8.7-10.6 
9.7 
8.5-11.6 
10.2 
8.4-10.8 
9.4 
9.1-11.4 
10.3 
9.3-11.6 
10.3 
9.0-11.7 
10.2 
9.2-11.6 
10.5 
7.3-10.4 
9.4 
9.0-11.3 
9.9 
9.3-11.2 
10.2 
9.2-12.0 
10.8 

10.1 

9.0-11.0 
10.1 
9.3-11.3 
10.4 
9.4-11.8 
10.8 
9.5-11.3 
10.4 
9.2-10.5 
9.8 
8.0-11.3 
10.2 
9.0-11.9 
10.1 
9.6-12.3 
10.7 
8.1-11.6 
9.1 
9.4-11.6 
10.5 
10.0-11.2 
10.4 
9.1-12.0 
10.8 

10.3 

9.3-11.3 
10.6 
9.6-11.2 
10.4 
9.8-11.3 
10.5 
9.3-11.7 
10.4 
9.2-10.7 
9.9 
9.1-11.1 
10.2 
9.3-10.7 
10.0 
9.3-11.4 
10.5 
7.9-11.1 
9.0 
10.4-12.5 
11.3 
10.0-11.2 
10.2 
11.5-13.2 
12.1 

10.4 

9.4-11.5 
10.7 
8.6-11.6 
10.4 
9.2-11.7 
10.  G 
9.3-11.3 
10.4 
9.5-11.7 
10.7 
9.3-10.6 
9.9 
9.0-11.6 
10.3 
9.0-12.1 
10.5 
8.2-11.1 
9.5 
9.9-11.3 
10.7 
9.4-11.6 
10.4 
9.7-13.0 
10.8 

10.4 

Buffalo  
Chicago 

Kansas  City.  .  . 
Louisville  

Newark 

New  Orleans  .  .  . 
New  York  .  .  . 

's'.s^ioii 

9.4 
8.4-11.7 
10.1 
8.1-9.9 
9.0 

Omaha  

St.  Louis  

Scran  ton.  . 

9.9-11.9 
10.6 
10.1-11.0 
10.5 

9.9 

8.5-10.3 
9.4 

Washington..  .  . 
Averaee.  . 

9.6 

SURFACE    MIXTURES. 


321 


Since  1896  these  irregularities  in  bitumen  have  grown  smaller 
and  the  average  percentage  of  bitumen  higher,  as  can  be  seen 
from  the  average  percentage  of  bitumen  in  the  mixtures  laid  under 
the  author's  supervision  as  long  ago  as  1897: 

AVERAGE  COMPOSITION,  SURFACE  MIXTURES,  1897. 


City. 

Bitu- 
men. 

Passing  Mesh. 

|o 

& 

2*4 
< 

200 

100 

80 

50 

40 

30 

20 

10 

St.  Louis,  Mo  

10.5 
10.4 
10.9 
10.8 
10.7 
10.1 

10.  e 

10.2 
10.1 
10.1 
10.5 
10.2 
11.4 
10.5 
10.0 
10.4 
10.6 
10.8 
10.6 
10.1 
10.5 
10.1 
10.4 
10.3 
10.8 
11.1 

10  R 

20.8 
18.9 
8.9 
14.0 
16.4 
14.0 
14.8 
14.5 
14.8 
14.2 
14.6 
15.5 
14.6 
16.0 
13.1 
13.7 
14.5 
12.4 
11.3 
12.7 
12.8 
13.2 
12.3 
13.1 
10.2 
10.9 

11.4 
13.1 
23.0 
16.4 
12.9 
15.2 
14.2 
13.9 
13.4 
12.5 
12.1 
10.9 
11.4 
9.7 
12.1 
11.5 
9.9 
11.3 
11.9 
10.0 
8.2 
7.6 
8.1 
6.9 
7.5 
6.4 

16.3 
13.7 
25.6 
16.5 
12.4 
14.4 
11.1 
13.2 
11.2 
9.2 
10.7 
8.8 
13.9 
9.8 
7.8 
14.6 
10.8 
13.7 
12.8 
8.9 
8.5 
7.3 
10.3 
5.0 
6.7 
12.7 

28.7 
30.9 
27.8 
32.4 
24.7 
38.7 
38.2 
37.5 
23.9 
24.6 
25.3 
24.5 
26.7 
28.7 
29.7 
41.5 
21.7 
41.2 
32.8 
25.9 
26.6 
30.5 
27.9 
34.1 
24.2 
41.0 

6.0 
4.6 
2.4 
4.5 
8.4 
4.9 
7.1 
6.9 
9.1 
10.8 
9.7 
9.4 
8.8 
9.2 
15.6 
5.1 
11.2 
4.3 
7.6 
11.9 
13.7 
15.6 
11.0 
19.9 
15.4 
8.6 

3.4 
3.4 

1.0 
2.4 
7.1 
1.9 
2.5 
2.9 
7.6 
10.2 
7.5 
9.8 
6.3 
8.1 
8.7 
2.1 
10.2 
24 
7.1 
10.4 
9.7 
12.2 
10.6 
6.8 
12.0 
5.9 

1.8 
2.6 
0.3 
1.5 
4.1 
0.6 
0.8 
0.6 
4.7 
5.6 
4.3 
6.5 
4.0 
4.2 
2.1 
0.7 
6.5 
1.7 
3.2 
5.9 
6.3 
2.7 
5.3 
2.8 
8.5 
1.9 

1.1 

2.5 
0.1 
1.5 
3.2 
0.3 
0.7 
0.2 
5.2 
2.8 
4.7 
4.3 
2.9 
3.7 
1.0 
0.4 
4.6 
2.2 
2.6 
4.1 
3.7 
0.8 
4.1 
1.1 
4.8 
1.4 

63° 
61° 
75° 
56° 
58° 
61° 
67° 
63° 
59° 
62° 
58° 
58° 
55° 
61° 
56° 
61° 
51° 
57° 
51° 
45° 
51° 
54° 
57° 
63° 
60° 
57° 

58° 

Kansas  City  Mo.  .  .  . 

Elmira,  N.  Y  

Chicago,  III  

New  York  N  Y 

Buffalo,  N.Y..4-B  Pit... 
"           "       3-B    "     . 
Niagara  Falls,  N.  Y.  . 

Boston,  Mass  

New  York,  N.  Y.,  Bronx. 
Yonkers,  N.  Y.*  

Newark  N  J 

Jersey  City  N  J 

Sioux  City,  Iowa  
Saginaw,  Mich  
Buffalo,  N.  Y.,  1-B  Pit... 
New  Orleans,  R.R.  Pit.  .  . 
Detroit,  Mich  

Pittston  Pa 

New  Orleans  La 

Wilkesbarre   Pa. 

Rockford  111  .         ... 

Scranton,  Pa  

Harrisburg,  Pa  

Washington  D  C 

Akron,  Ohio.  . 

Average  

*  Retained  on  10-mesh,  .5%. 

Experience  has  shown,  however,  that  in  these  surfaces,  although 
the  average  percentage  of  bitumen  reached  10.5,  it  was  in  most 
cases  too  hard,  averaging  58 ;  which  has  resulted  in  some  cracking. 
In  subsequent  years,  therefore,  it  has  been  the  practice  to  use 
softer  asphalt  cement.  The  results  have  been  very  satisfactory. 

Too  small  an  amount  of  bitumen  in  a  mixture  permits  the 
easy  entrance  or  absorption  of  water,  which  eventually  disin- 
tegrates and  rots  the  surface.  It  reduces  the  tensile  strength 


322  THE  MODERN  ASPHALT  PAVEMENT. 

and  prevents  the  accommodation  of  the  surface  to  the  contrac- 
tion of  the  mineral  aggregate,  which  follows  a  rapid  fall  of  tem- 
perature, as  this  can  only  be  met  by  the  elongation  of  the  bitu- 
men. In  both  of  these  ways  lack  of  bitumen  is  a  direct  cause  of 
cracking  and  deterioration  of  pavements. 

Analyses  of  specimens  of  old  surface  from  Omaha,  grouped 
and  arranged  according  to  their  condition,  show  that  the  badly 
cracked  pavements  in  that  city  contain  the  least  bitumen  and 
the  better  pavements  the  most,  as  appears  from  the  following 
figures : 

AVERAGE  BITUMEN  IN  OMAHA  ASPHALT  SURFACES. 

Good 10.0% 

Medium 9.4 

Badly  cracked 8.6 

The  results  of  the  examination  of  the  surfaces  collected  in 
1894  and  of  the  data  available  at  that  time  having  shown  nothing 
more  than  the  fact  that  there  was  no  uniformity  in  the  way  the 
mixture  was  made  before  then,  and  that  it  would  be  necessarv 
to  extend  the  investigation  still  further  to  find  which  was  the 
most  desirable  composition,  this  work  was  continued  as  oppor- 
tunity offered  during  a  period  extending  over  two  years  and  with 
extremely  interesting  results,  which  were  published  in  Bulletin 
No.  1  of  the  Office  of  the  Superintendent  of  Tests  of  the  Barber 
Asphalt  Paving  Company,  in  March  1896,  the  substance  of  which 
was  as  follows: 

"  The  attention  of  the  author  was  attracted,  as  long  ago  as 
1889,  to  a  particularly  good  asphalt  surface  on  Vermont  Avenue, 
in  Washington,  D.  C.,  which,  although  subjected  to  light  traffic, 
had  had  scarcely  a  repair  after,  at  that  time,  ten  years'  service. 
An  analysis  of  this  surface  gave  the  following  results : 

"Bitumen 11.3% 

Passing  200-mesh  sieve 16.0 


100- 
80- 
50- 
40- 
30- 
20- 
10- 


8.7 

5.2 

32.0 

16.4 

6.0 

2.7 

1.7 


100.0 
Density 2.18 


SURFACE    MIXTURES.  323 

"  The  high  percentage  of  bitumen  and  of  dust,  both  unusual 
at  the  time  the  surface  was  examined,  led  to  the  conclusion  that 
the  desirable  properties  of  this  surface  were  due  to  the  presence 
of  plenty  of  bitumen  and  dust.  In  order  to  confirm  this,  several 
other  surfaces  were  selected  in  Washington  which  were  typically 
good  or  bad,  and  it  was  found  that  the  best  were  characterized 
by  a  similar  composition  to  that  of  the  Vermont  Avenue  surface, 
while  the  inferior  were  deficient  in  both  asphalt  cement  and  dust. 
An  inquiry  as  to  the  conditions  under  which  the  Vermont  Avenue 
surface  was  laid  showed  that  the  sand  in  use  was  from  a  pit  and 
contained  much  fine  material,  on  which  account  it  was  eventually 
abandoned. 

"  In  1893  attention  was  called  to  the  excellent  character  of 
the  asphalt  surface  on  Court  Street  in  Boston,  which  had  sustained 
successfully  a  very  heavy  traffic.  The  surface  mixture  was 
examined  by  the  author  and  found  to  have  the  following  compo- 
sition : 

"  Bitumen 11 . 7% 

Passing  200-mesh  sieve 14.5 

"       100-    "        "   11.2 

"         80-    "        "     24.1 

"         50-    "        "    20.5 

"         40-    "        "   5.8 

"         30-    "        "    4.6 

"         20-    "        "   4.0 

"         10-    "        "   3.6 

100.0 

"  In  this  mixture  high  percentages  of  bitumen,  of  dust  and  of 
fine  sand  were  found,  which  was  in  confirmation  of  the  original 
conclusion  that  the  Vermont  Avenue  surface  in  Washington  wore 
well  because  it  contained  high  percentages  of  these  materials. 
These  results  led  to  the  suggestion  that  the  inquiry  should  be 
extended  to  a  collection  of  representative  surfaces  from  various 
parts  of  the  country.  This  was  undertaken  and  led  to  the  same 
general  conclusion,  namely,  that  surfaces  carrying  the  most  bitu- 
men and  dust  or  filler  are  the  most  satisfactory. 

"  In  1895  the  inquiry  was  extended  still  further,  and  an  exam- 
ination of  the  street  surfaces  laid  in  a  western  city  during  the 


324 


THE  MODERN  ASPHALT  PAVEMENT. 


period  extending  from  1888  to  that  year,  some  of  which  were  much 
more  satisfactory  than  others,  was  made.  The  results  of  the 
analyses  of  surfaces  representing  different  years'  work  were  as 
follows : 


1888 

1889 

1890 

1891 

1892 

1893 

1894 

1895 

"  Bitumen 

9  85 

10  35 

9  35 

9  05 

10  55 

9  85 

9  35 

9  50 

Passing  200-mesh  sieve.  .  .  . 

9.00 

9.60 

7.50 

10.60 

9.25 

9.00 

11.40 

10.95 

100- 

8.80 

25.45 

10.10 

9.60 

5.80 

6.30 

16.60 

13.95 

80- 

10.20 

23.05 

10.50 

14.50 

6.65 

5.40 

16.30 

17.50 

50- 

26.00 

20.05 

20.00 

30.20 

26.50 

36.30 

21.50 

31.00 

40-                   

12.30 

4.55 

12.70 

8.20 

14.40 

10.80 

6.10 

4.95 

30- 

11.90 

4.05 

13.90 

6.90 

12.55 

8.20 

7.80 

6.40 

20- 

6.60 

2.80 

7.60 

5.00 

8.25 

6.50 

6.00 

2.70 

"         10- 

3.35 

2.10 

8.35 

5.95 

6.05 

7.65 

4.95 

3.08 

"If  these  results  are  grouped  more  closely,  calling  200-mesh 
material  dust,  100-  and  80-mesh  material  fine  sand,  50-  and  40-mesh 
medium,  and  30-,  20-,  and  10-mesh  coarse  sand,  the  analyses  catch 
the  eye  more  quickly. 


1888 

1889 

1890 

1891 

1892 

1893 

1894 

1895 

"  Bitumen  

9.85 
9.00 
19.00 
40.30 
21.85 

10.35 
9.60 
46.50 
24.60 
8.95 

9.35 

7.50 
20.60 
32.70 
29.85 

9.05 
10.60 
24.10 
38.40 
17.85 

10.55 
9.25 
12.45 
40.90 
26.85 

9.85 
9.00 
11.70 
47.10 
22.35 

9.35 
11.40 
32.90 
27.60 
18.75 

9.50 
10.95 
31.45 
35.95 
12.18 

Dust  

Fine  sand 

Medium  sand                  .  .  . 

Coarse  sand                       .  .  • 

"The  characteristics  of  these  surfaces  as  noted  on  the  streets 
were: 

"  1888 Soft;  pushes  and  calks. 

1889 Considered  one  of  the  best  mixtures. 

1890 Calks  badly. 

1891 Calks  badly. 

1892 Calks  badly. 

1893 Calks  worst  of  all;  very  mushy. 

1894 Hardly  marked;  very  stable. 

"The  1894  mixture  is  the  only  one  which  has  produced  a  surface 
which  is  reasonably  free  from  calking  in  hot  weather.     Of  the 


SURFACE    MIXTURES.  325 

1895  surfaces  we  cannot  judge  until  another  year,  although  they 
at  present  are  very  promising  and  probably  quite  as  good  as  those 
of  1894.1  The  1889  surfaces  are  in  better  form  than  the  surfaces 
of  years  prior  to  1894.  Those  of  1891,  1892,  and  1893  are  so  yield- 
ing as  to  be  a  mass  of  calk  marks  hi  summer.  How  this  occurs  is 
seen  from  the  differences  which  are  brought  out  by  analyses.  The 
1888,  1890,  1891,  1892,  and  1893  surfaces  are  deficient  in  fine  sand 
as  compared  to  those  of  1894,  and  this  is  especially  the  case  with 
those  of  1892  and  1893,  where  there  is  but  12.45  and  11.70  per  cent, 
respectively,  of  fine  material.  They  do  not  carry  enough  sand 
grains  of  this  size  to  make  the  surface  dense,  and  of  course  con- 
versely they  have  too  much  coarse  material.  It  is  apparent,  there- 
fore, that,  with  the  available  sand,  the  grading  must  be  so  arranged 
that  the  coarse  part  shall  not  run  as  high  as  20  per  cent,  preferably 
about  15  per  cent,  and  the  fine  shall  reach  about  30  per  cent,  the 
dust  being  about  11  per  cent,  to  give  a  stable  surface.  The  bitumen 
in  these  mixtures  is  too  low  when  compared  with  the  amount  found 
necessary  for  good  surfaces  in  most  cities,  but  here  it  was  due  to 
peculiarities  in  the  sand,  owing  to  which  it  will  not  carry  more, 
and  is  therefore  not  as  serious  a  defect  as  it  would  be  in  some 
other  places. 

"As  a  whole  the  experience  in  this  city  was  very  encouraging 
in  its  confirmation  of  previous  conclusions,  and  sufficiently  so  to 
render  an  attempt  to  follow  them  out  in  practice  in  other  places 
desirable." 

The  bulletin  then  goes  on  to  present  two  illustrative  cases 
where  an  explanation  had  been  sought  for  the  good  or  bad  wearing 
properties  of  asphalt  surfaces: 

"  In  New  York  there  has  been  during  the  present  winter  (1896) 
some  scaling  of  surfaces  laid  in  the  autumn  of  1895,  whereas  others 
have  shown  nothing  but  the  best  results.  Typical  of  these  were 
surfaces  on  Fifth  Avenue  at  Fifty-ninth  Street  and  on  Eighth 
Avenue  at  Twenty-eighth  Street.  Analyses  were  made  of  speci- 
mens of  these  surfaces,  which  quickly  explained  the  differences  in 
behavior.  The  results  were  as  follows: 

1  At  the  present  time  it  can  be  seen  that  the  mixtures  of  1895  have  proved 
as  desirable  as  it  was  expected  they  would. 


326 


THE   MODERN    ASPHALT    PAVEMENT. 
NEW   YORK   MIXTURE   LAID   IN  1895. 


Per  Cent. 

Per  Cent. 

"  Bitumen 

9.8 
7.3 
5.9  \u  7 
8.8/14'7 
24.4 
12.4 
9.1) 
10.7^30.6 
10.8) 
.8 

11.1 
9.8 

ll.llio 

7.5/18 
28.6 
6.6 
10.3  ) 
8.0^25 
7.0J 

.6 
.3 

Passing  200-me 
100- 
80- 
50- 
40- 
30- 
20- 
10- 
Retained  on  10 

*sh  sieve  

<  i 

1  1 

<  t 

a 

K 

tt 

it 

100.0 

100.0 

"  The  same  striking  contrast  between  a  good  surface  and  a 
poor  one  is  here  again  well  illustrated  in  the  difference  in  bitumen 
and  fine  material  in  the  two  specimens. 

"  Again  the  unsatisfactory  surfaces  from  St.  Louis,  samples  of 
which  were  sent  in  recently  for  examination,  show  that  a  coarse 
mixture  is  an  inferior  one  and  likely  to  scale.  The  results  of  an 
examination  of  the  St.  Louis  surfaces  were  as  follows.  See  results 
given  in  first  two  tables  on  page  327. 

"In  this  way  the  original  conclusions  of  earlier  years  have 
been  confirmed,  and  it  has  become  the  present  policy  to  work  upon 
the  lines  above  indicated  in  laying  surface.  While  nothing  abso- 
lutely fixed  can  be  suggested  as  a  universal  mixture,  perhaps  for 
the  present  the  following  may  be  considered  as  an  ideal  towards 
which  to  work. 


"Bitumen  

10.0% 

or  above 

Passing 

200-mesh 

sieve  

10.0% 

1  1 

1  1 

tt 

100- 

1  1 

1  1 

10.0% 

tt 

tt 

tt 

80- 

1  1 

tt 

20.0% 

tt 

tt 

tt 

50- 

tt 

tt 

24.0% 

1  1 

tt 

ii 

40- 

it 

tt 

10.0% 

tt 

tt 

n 

30- 

it 

1  1 

8.0% 

tt 

tt 

tt 

20- 

1  1 

it 

5.0% 

tt 

tt 

tt 

10- 

tt 

tt 

3.0% 

1  1 

tt 

"  The  grading  should  not,  apparently,  be  stretched  too  far  as 
in  such  a  case  but  little  asphalt  cement  can  be  gotten  in,  and  the 
surface  will  lack  elasticity. 


SURFACE    MIXTURES. 


327 


ST.   LOUIS  SURFACES  OF  1892. 


Per  Cent. 

Per  Cent. 

"Bitu 
Passin 

tt 

it 
tt 
it 
tt 
tt 

9.7 

6.*9 

9.7 
17.7) 
20.  2V  56.  5 
18.6) 

100.0 

10.0 
7.1 
7.311?8 
10.  5/17-* 
19.0 
8.4 
13.9) 
12.4V37.7 
11.4) 

g  200-mesh  sieve  

100-              "    

80-              "    . 

50-              "    

40-              "    

30-             "   

20-             M  ... 

10-    "        "   

100.0 

ST.  LOUIS  SURFACES  OF  1893. 


Per  Cent. 

Per  Cent. 

Per  Ont. 

Per  Cent.N 

Per  Cent. 

"  Bitumen. 

9.2 

10.6 

9.4 

10.2 

9.3 

Passing  200 

2.8 

5.5 

7.0 

6.3 

6.6 

"       100 
80 

9.4  r19-0 

si}13-0 

S.'SJ13'8 

5.61    9  g 
4.3J    y'9 

5.61    Q3 
3.7/    9'3 

50 

37.0 

27.3 

17.8 

18.4 

10.2 

"         40 

10.7 

11.1 

11.1 

12.7 

10.0 

30 
"         20 
"         10 

10.8) 
5.7  f-21.3 

4.8) 

15.3) 
9.6  [32.5 
7.6) 

18.1  ) 
15.5  V40.9 
7.3) 

15.5) 
13.2V42.5 
13.8) 

21.1  ) 
20.4  V54.  6 
13.1  ) 

100.0 

100.0 

100.0 

100.0 

100.0 

"  Finally,  it  must  be  remembered  that  many  mixtures  which 
are  quite  different  from  the  fine  ones  which  have  been  mentioned 
have  furnished  good  surfaces  for  light  traffic.  In  Washington,  D.  C., 
for  instance,  a  recent  mixture  (1896)  analyzed  as  follows,  and 
will,  no  doubt,  serve  entirely  well  there: 

"Bitumen 11.4% 

Passing  200-mesh  sieve 7.2 


100- 
80- 
50- 
40- 
30- 
20- 
10- 


2.9 
3.1 

14.4 
16.9 
19.1 
16.4 
8.6 

100.0 


"  In  the  same  way  many  coarse  streets  in  Buffalo  have  served 
as  well  as  could  be  desired. 


328  THE    MODERN    ASPHALT    PAVEMENT. 

"  In  conclusion,  attention  must  be  called  to  the  fact  that  a 
high  percentage  of  bitumen  is  not  safe  in  a  mixture  which  is  defi- 
cient in  dust  and  fine  sand,  especially  when  it  is  to  meet  heavy 
traffic,  because  such  a  surface  is  unstable  without  the  material 
which  gives  it  stiffness  and  capacity  to  resist  pushing  and  mark- 
ing. This  is  the  reason  the  use  of  large  percentages  of  asphalt 
cement  in  some  cases  has  been  the  cause  of  trouble  and  has  led 
to  the  use  of  mixtures  deficient  in  asphalt  cement  for  streets  of 
heavy  traffic.  In  most  cases,  with  plenty  of  dust  and  fine  sand, 
the  per  cent  of  asphalt  cement  in  the  mixture  with  steam  re- 
fined Trinidad  asphalt  can  be  carried  well  above  15  per  cent. 

"  CLIFFORD  RICHARDSON, 

"Superintendent  of  Tests. 

"  Long  Island  City,  N.  Y.,  March  10,  1896." 

Soon  after  the  appearance  of  this  bulletin  the  author  carried 
out  the  ideas  contained  in  it  in  laying  a  Trinidad  lake  asphalt 
pavement,  on  the  King's  Road  in  Chelsea,  London,  England. 
The  composition  of  this  mixture  was  as  follows: 

Bitumen 10.8% 

Passing  200-mesh  sieve 13 . 6 

"       100-    "        "   7.3 

"         80-    "        "   22.5 

"         50-    "        "   25.5 

"         40-    "        "   8.9 

"         30-    "        "   6.6 

"         20-    "        "   3.0 

"         10-    "        "   .  1.8 


100.0 

As  this  surface  resisted  entirely  successfully  the  heavy  traffic 
and  fogs  of  London,  where  previous  attempts  with  coarser  sand 
and  less  filler  had  failed,  it  seemed  to  settle  the  fact  that  the  con- 
clusions drawn  in  the  bulletin  were  correct,  and  from  that  time 
to  the  present  all  the  work  under  the  supervision  of  the  author 
on  streets  of  much  travel  has  been  done  with  surface  mixtures 
made  on  these  lines. 

After  the  London  work  the  next  important  surface  which  was 
laid  was  that  on  Fifth  Avenue,  in  New  York.  This  has  proved 
successful.  Its  average  composition  is  as  follows: 


SURFACE    MIXTURES. 


329 


Bitu- 
men. 

Passing  Mesh 

200 

100 

80 

50 

40 

30 

20 

10 

1896  .  . 

10.8 
10.6 

15.4 
17.4 

10.5 
12.3 

10.7 
11.1 

22.3 
23.3 

10.9 
8.8 

8.9 
8.0 

4.9 
4.7 

5.6 
3.7 

1897  

FOR     COMPARISON. 


London.  . 

10.8 

13.6 

7.3 

22.5 

25.5 

8.9 

6.6 

3.0 

1.8 

After  from  twelve  to  thirteen  years'  use  the  surfaces  laid  in  Lon- 
don and  that  on  Fifth  Avenue,  New  York,  have  proved  them- 
selves most  satisfactory. 

Since  the  year  1896  the  asphalt  pavements  laid  by  the  Barber 
Asphalt  Paving  Company  have  been  constructed,  as  a  rule,  in  a 
similar  way  to  that  which  has  been  described;  but  there  has  been  a 
decided  improvement  in  the  character  of  the  work  with  each  suc- 
ceeding year,  as  can  be  seen  by  comparing  the  average  com- 
position of  mixtures  laid  in  1896  in  several  important  cities  with 
those  laid  in  the  same  places  in  1899  and  in  1904. 

BITUMEN  AND  MINERAL  AGGREGATE. 
1896. 


City. 

Bitu- 
men. 

Passing  Mesh 

200 

100 

80 

50 

40 

30 

20 

10 

Boston 

9.9 
9.7 
10.2 
9.4 
10.3 
10.3 
10.2 
10.5 
9.4 
9.9 
10.2 
10.8 

10.1 

10.9 
6.7 
8.9 
12.4 
10.9 
10.0 
10.4 
12.9 
9.6 
14  3 
9.9 
7.8 

13.0 
5.6 
12.3 
7.9 
4.9 
8.0 
8.4 
10.4 
10.8 
9.4 
8.5 
6.0 

12.9 
18.1 
16.9 
15.8 
11.3 
9.1 
10.1 
10.6 
18.4 
13.3 
11.0 
9.3 

24.4 
44.4 
27.9 
36.7 
48.3 
22.4 
28.3 
22.8 
30.6 
33.0 
26.1 
27.8 

9.9 
7.3 
8.3 
6.1 
7.3 
13.3 
13.2 
11.9 
8.3 
10.3 
13.5 
17.9 

8.3 
3.4 
5.8 
4.8 
3.3 
11.6 
11.2 
9.5 
5.9 
6.1 
11.0 
13.1 

5.4 
1.9 
4.7 
3.3 
1.8 
7.5 
5.4 
5.8 
3.7 
2.6 
5.9 
4.8 

5.4 
2.7 
5.0 
3.5 
1.9 
7.7 
2.7 
55 
3.2 
1.1 
3.8 
2.5 

Buffalo  1-B.         .    . 

Chicago  Pit.  1  

Louisville 

Newark  . 

New  Orleans.  .  .  . 

New  York   

Omaha  

St   Louis 

Scran  ton  . 

Washington  
Average  per  cent  .  .  . 

330 


THE    MODERN    ASPHALT  PAVEMENT. 


BITUMEN  AND  MINERAL  AGGREGATE. 

1897. 


City. 

Bitu- 
men. 

Passing  Mesh 

200 

100 

80 

50 

40 

30 

20 

10 

Boston.  .  .      . 

10.1 
10.4 
10.8 
10.4 
9.8 
10.2 
10.1 
10.7 
9.1 
10.5 
10.4 
10.8 

10.3 

14.8 
13.7 
14.0 
18.9 
13.4 
15.5 
12.7 
16.4 
13.3 
20.8 
12.3 
10.2 

13.4 
11.5 
16.4 
13.1 
5.8 
10.9 
10.0 
12.9 
12.7 
11.4 
8.1 
7.5 

11.2 
14.6 
16.5 
13.7 
9.5 
8.8 
8.9 

23.9 
41.5 
32.4 
30.9 
49.1 
24.5 
25.9 

9.1 
5.1 
4.5 
4.6 
6.8 
9.4 
11.9 

7.6 
2.1 
2.4 
3.4 
2.9 
9.8 
10.4 

4.7 
0.7 
1.5 
2.6 
1.6 
6.5 
5.9 

5.2 
0.4 
1.5 
2.5 
1.1 
4.3 
4.1 
3.2 
2.3 
1.1 
4.1 
4.8 

Buffalo  1-B.     .    . 

Chicago  

New  Orleans  

•NT              WvWlr 

IN  ew  i  OFK  
Omaha.  ... 

15.9 
16.3 
10.3 
6.7 

32.3 

28.7 
27.9 
24.2 

6.7 
6.0 
11.0 
15.4 

5.1 
3.4 
10.6 
12.0 

2.6 
1.8 
5.3 

8.5 

St.  Louis       .    ... 

Scranton  

Washington  

Average  per  cent  .  .  . 

1898. 


10.6 

14  7 

13.6 

12.8 

25  3 

9  8 

6.7 

3  9 

2  6 

Buffalo  1-B 

10  4 

14  1 

12  6 

17  2 

35  9 

5  5 

2  5 

1  4 

0  1 

Chicago 

10  5 

13  2 

15  5 

13  2 

33  6 

8  4 

3  0 

1  9 

0  6 

Kansas  City  

10  4 

14  6 

12  4 

14  0 

28  6 

7  4 

5  8 

4  0 

2  g 

Louisville  

9  9 

15  0 

10  6 

10  2 

30  9 

9  8 

6  6 

3  4 

3  6 

Newark  

10  2 

11  6 

11  2 

7  5 

18  5 

12  9 

10  6 

10  4 

6  8 

New  Orleans  

10.0 

11  1 

7  8 

10  0 

31  1 

14  2 

10  0 

3  7 

2  1 

10  5 

13.7 

13.1 

13  4 

22  6 

10.0 

7.6 

5  6 

3  5 

Omaha 

9  0 

11  8 

14  2 

17  5 

29  9 

7  3 

4  8 

3  3 

2  2 

St   Louis 

11  2 

13  2 

9  7 

14  7 

37  2 

57 

3  8 

2  7 

1  7 

Scranton  .        

10  2 

12  4 

10  8 

10  5 

26  6 

11  8 

8  9 

5  2 

3  5 

Washington  

12.1 

12  1 

8  2 

7  6 

25  6 

17  6 

9  4 

4  6 

2  8 

Average  per  cent.  .  . 

10.4 

1899. 


Boston  .    .       ... 

10  7 

14  5 

12  1 

9  3 

22  2 

14  0 

7  5 

5  7 

4  0 

Buffalo  1-B  

10  4 

13  2 

10  6 

16  7 

37  3 

6  3 

2  4 

1  7 

1  3 

Chicago  

10  6 

11  5 

14  3 

15  5 

34  5 

7.6 

2  8 

1  8 

1  4 

Kansas  City  
Louisville 

10.4 
10  7 

12.1 
15  5 

9.2 

7  1 

13.9 
4  6 

39.3 
36  9 

7.1 
19  3 

3.6 
3  0 

2.7 
1  6 

1.7 
1  i 

Newark 

9  9 

14  8 

13  7 

9  6 

11  6 

11  3 

9  7 

10  5 

8  9 

New  Orleans  .... 

10  3 

12  6 

11  1 

9  3 

25  5 

17  0 

6  9 

5  1 

2  2 

New  York   

10  5 

13  0 

12  7 

12.6 

23  9 

12  1 

6  6 

5  3 

3  3 

Omaha  

9.5 

13.4 

13.3 

12.6 

25.9 

11.7 

5.6 

4.7 

3  3 

10.7 

12.3 

12.2 

11.0 

29.7 

11.3 

5.4 

4.3 

3.1 

Scranton                . 

10  4 

13  0 

11  6 

10  9 

22  9 

15  0 

7  7 

5  2 

3  3 

Washington  

10  8 

12.7 

7.6 

5.2 

17.4 

20  0 

10  0 

8.7 

7.6 

Average  per  cent.  .  . 

10.4 

SURFACE    MIXTURES.  331 

AVERAGE  COMPOSITION  SURFACE  MIXTURE.     1904. 


aty. 

Bitu- 
men. 

Pa* 

ing  U 

e.-h 

2 
1 

age 
net  ration 
A.  C.  1 

200 

100 

80 

50 

40 

30 

20 

10 

i 

r* 

Alexandria,  La.  .  .  . 
Allegheny,  Pa  
Auburn  Ind  

10.0% 
11.2 
10  5 

11.0% 
12.8 
12.5 

18% 
5 
13 

7% 
9 
1? 

19% 
42 

?8 

15% 
11 
9 

13% 
4 
6 

5% 
4 

2% 
5 

55° 

62 
68 

Boston,  Mass  

11.2 

12.8 

10 

1? 

3?, 

12 

5 

3 

? 

64 

Buffalo,  N.  Y  

10.4 

17.6 

1? 

9 

?« 

7 

4 

3 

7 

5% 

6? 

Chicago  111 

10  5 

11  5 

16 

17 

34 

5 

? 

2 

? 

61 

Cincinnati,  Ohio.  .  . 
Decatur  111  

10.2 
11  4 

12.8 
15.6 

11 

10 

13 

8 

29 

?7 

13 
11 

6 

6 

3 
5 

2 
5 

i 

54 
63 

Des  Moines,  Iowa.  . 
Detroit  Mich 

11.0 

10  7 

12.0 
10  3 

9 
12 

16 

12 

30 
33 

9 
10 

8 
7 

3 
3 

2 
? 

71 

72 

Ft.  Dodge,  Iowa.  .  . 
Ft.  Wayne,  Ind  
Grand  Rapids,  Mich. 
Harrisburg,  Pa  
Kansas  City,  Mo.  .  . 
New  York,  N.  Y.  .  . 
Los  Angeles,  Cal.  .  . 
Louisville,  Ky  
New  Albany,  Ind.  .  . 
New  Orleans,  La.  .  . 
Niagara  Falls,  N.  Y. 
Omaha  Neb 

10.9 
10.6 
10.2 
10.6 
10.3 
10.9 
11.0 
11.2 
10.8 
10.1 
10.3 
10  9 

12.1 
11.4 
11.8 
13.4 
21.7 
14.1 
12.0 
15.8 
17.2 
10.9 
12.7 
13.1 

12 
11 
11 
6 
18 
11 
14 
12 
7 
15 
11 
7 

13 
12 
10 
8 
13 
10 
12 
8 
5 
13 
13 
13 

27 
27 
23 
32 
16 
28 
20 
26 
23 
23 
26 
39 

13 
14 
12 
15 
6 
13 
11 
13 
17 
14 
10 
6 

6 
7 
11 
7 
6 
7 
8 
7 
12 
8 
9 
4 

3 

5 
6 
5 
6 
4 
8 
4 
6 
4 
3 
4 

2 
2 
4 
3 
3 
2 
4 
3 
2 
2 
4 
3 

i 
i 

i 

64 
66 
62 
66 

68 

53 
65 
54 
67 
69 

Ottawa  Ont 

10  6 

15.3 

20 

11 

27 

7 

4 

4 

1 

58 

Pittsburg  Pa.  .  .  . 

10  4 

12.6 

7 

6 

42 

12 

5 

3 

?, 

67 

Sandusky,  Ohio.  .  .  . 
Seattle,  Wash  
Spokane,  Wash.  .  .  . 
St.  Louis,  Mo  

10.4 
12.3 
12.9 
11.3 

8.6 
12.7 
11.1 
15.7 

13 
14 
14 
15 

12 
11 
11 
14 

28 
25 
22 
27 

12 
11 
8 
6 

7 
7 
9 
5 

5 

4 

7 
4 

4 
3 
5 
2 

•  •  • 

67 
80 
77 
75 

St.  Paul  Minn  .  . 

10  9 

14  1 

1? 

14 

31 

10 

5 

?, 

1 

74 

Tacoma,  Wash  
Toronto,  Ont  
Trenton,  N.  J. 

11.9 
10.7 
10  5 

12.1 
16.3 
10.5 

13 
21 
9 

10 
14 
14 

24 
27 
29 

13 

6 
14 

8 
3 

8 

5 

I 
3 

3 

1 
2 

... 

76 
61 
73 

Walla  Walla,  Wash. 
Wichita  Kan 

13.4 
10  3 

7.6 
11.7 

14 
10 

12 
16 

27 
3? 

8 
10 

8 
5 

9 
3 

1 

?, 

... 

80 

Average  

10  9 

66 

The  general  improvement  and  greater  uniformity  reached  by 
experience  between  1896  and  1899  and  1899  and  1904  is  marked 
in  several  particulars.  The  average  per  cent  of  bitumen  in  the 
more  recent  mixtures  is  at  a  far  better  figure,  10.9,  because  the 
grading  in  the  late*  <nineral  aggregate  is  more  satisfactory,  since 


332  THE  MODERN  ASPHALT  PAVEMENT. 

it  holds  more  200-mesh  dust  and,  as  a  rule,  a  better  percentage 
of  100-  and  80-mesh  sand.  In  some  cases,  of  course,  the  sand 
grading  could  still  be  improved  upon  in  this  direction,  but  this  is 
the  case  only  where  no  suitable  fine  sand  was  available  within 
reasonable  distances,  as  in  Washington  and  Louisville,  while  a 
falling  off  of  the  100-  and  80-mesh  grains  in  New  York  in  1904 
is  due  to  inability  to  find  such  sand,  this  material  being  derived 
in  1899  from  ballast  coming  to  the  port,  none  of  which  is  now  to 
be  had.  The  New  York  surface  mixture  of  1904  is,  therefore, 
not  as  satisfactory  as  it  was  in  the  former  years. 

The  New  York  mixture  of  1899  was  regarded  at  that  time  as 
an  unexceptional  one,  and  it  was  decided  to  consider  it  a  standard 
for  mixtures  on  streets  of  any  traffic  for  the  remainder  of  the  country. 
In  round  numbers  the  composition  of  this  mixture  and  of  the  sand 
of  which  it  was  composed,  regardless  of  the  small  amount  of  200- 
mesh  material  which  it  contained,  was  as  follows: 

Sand. 

Bitumen 10 . 5% 

Passing  200-mesh  sieve 13.0 


100- 
80- 
50- 
40- 
30- 
20- 


13.0  17.0% 

13.0  17.0 

23.5  30.0 

11.0  13.0 

8.0  10.0 

5.0  8.0 


10-    "        "    3.0  5.0 


100.0  100.0 

With  the  object  of  explaining  to  the  practical  man,  the  super- 
intendent or  yard  foreman,  the  features  of  such  a  standard  mix- 
ture it  was  considered  from  the  point  of  view  of  consisting  of  a 
mineral  aggregate  composed  of  sand  and  dust  and  a  proper  per- 
centage of  bitumen.  The  mineral  aggregate  must  be  regarded 
as  being  made  up  of  three  elements — the  fine  sand,  which  is  the 
most  important,  the  coarse  sand,  which  is  desirable,  and  the  dust 
or  filler,  which  is  absolutely  necessary.  The  mineral  aggregate  of 
a  standard  mixture  may,  therefore,  be  considered  from  the  following 
points  of  view: 

1st  point — 100-  and  80-mesh  sand 17-1- 17 =34% 

2d       "    — 10-,  20-,  and  30-mesh  sand 10  +  8  +  5  =  23 

3d       « t    — Filler  +  200  sand.     Dust  +  fine  sand . .  =17 


SURFACE    MIXTURES. 


333 


Or  for  the  complete  surface  mixtures: 

1st  point— 100  and  80  sand 13  +  13=26% 

2d       "    —10,  20,  and  30  sand 3  +  5  +  8  =  16 

3d       "    — Filler  +  200  sand =13 

4th     "    — Bitumen =10.5 

Or  these  points  may  be  expressed  in  one  of  the.  following  ways. 
ASPHALT  SURFACE  MIXTURE. 

Bitumen 
10.5% 
(4th  point) 


FUler,  13.0% 

Correct   surface 

(3d  point) 

mixture,  100% 

Mineral  aggre- 

gate, 89.5% 

(1st  point) 

(2d      "    ) 

,      (3d     "    ) 

Sand,  76.5% 

.  • 

(1st  point) 

(2d     "    ) 

26.0% 


Mesh. 
100.. 13.0 

80.. 13.0 
(1st  point) 

50 23.5% 

40 11.0% 

30. ..8.0 

20...  5.  Oj-16.0% 


ASPHALT  SURFACE  MIXTURE. 


30. ..8.0) 
20...5.0V16. 
10... 3.0) 
(2d  point) 


Composition, 

i  —  4th  point 

Mineral 
aggre- 
gate, 
89.5% 

Correct 
asphalt 
mixture, 
100% 

Filler+  200  sand  13 

.0  —  3d  point  ' 

Sand, 

76.5% 

^'^oKo-Ut  point 
50  23.5 

40  11.0 

30  8.0) 

20          .  5  0>16.0  —  2d  point 

10..       .  3.0> 

334  THE  MODERN  ASPHALT  PAVEMENT. 

The  surface  mixture,  therefore,  may  be  regarded: 

1st.  As  a  whole. 

2d.  As  a  mixture  of  bitumen  and  a  mineral  aggregate. 

3d.  As  a  mixture  of  bitumen,  filler,  and  sand. 

4th.  As  a  mixture  of  bitumen,  filler,  100-  and  80-mesh  sand 
and  10-,  20-,  and  30-mesh  sand  in  suitable  proportions. 

For  example  take  a  New  York  mixture: 

1st.  New  York  mixture. 

2d.  10.5  per  cent  bitumen,  89.5  per  cent  mineral  aggregate. 

3d.  10.5  per  cent  bitumen,  13.0  per  cent  dust,  76.5  per  cent  sand. 

4th.  Bitu-       200      100          80       50         40       30       20        10 

men,      Dust,     » , •  » . , 

10.5      13.0  26.0          23.5      11.0  16.0 

or 

10.5      13.0     13.0     13.0     23.5     11.0     8.0    5.0     3.0 

In  forming  an  opinion,  therefore,  of  an  old  or  new  surface  mix- 
ture it  becomes  evident  that  the  four  points  which  have  been  de- 
scribed must  be  considered.  These  points  may  be  differentiated 
from  the  composition  of  an  old  mixture  or  combined  to  form  a 
new  one. 

The  primary  consideration  is  the  sand  and  the  first  point  that  it 
shall  contain  a  normal  and  sufficient  amount  of  100-  and  80-mesh 
material.  This  was,  and  undoubtedly  is  to-day,  the  most  essential 
feature  in  making  a  satisfactory  mixture.  It  is  essential  because 
without  this  fine  sand  the  mixture  is  porous  and  open,  and  more 
particularly  because,  unless  it  is  present,  a  sufficient  amount  of  dust 
or  filler  cannot  be  used.  The  fine  sand  prevents  the  dust  from 
balling  up  and  making  a  lumpy  mixture  and,  as  will  eventually 
appear,  the  larger  the  amount  of  fine  sand  the  more  dust  can  be 
introduced  without  difficulty.  In  the  earlier  mixtures,  1880  to 
1896,  a  large  percentage  of  dust  could  seldom  be  used,  although 
the  attempt  was  often  made,  as  the  resulting  mixture  was  difficult 
to  handle  and  rake. 

The  second  point  or  consideration  lies  also  in  the  sand  grading 
and  is  the  regulation  of  the  amount  of  the  10-,  20-,  and  30-mesh 
sand  grains.  In  the  Fifth  Avenue  mixture  this  material  amounted 


SURFACE    MIXTURES.  335 

to  16  per  cent.  It  was  unavoidable  there,  owing  to  the  character 
of  the  sand  available,  but  was  believed  to  be  desirable  in  several 
ways.  In  the  first  place,  it  seemed  to  fill  the  place  taken  by  broken 
stone  in  hydraulic  concrete,  and  to  carry  the  traffic,  so  to  speak. 
In  the  second  place,  it  gave  a  less  slippery  surface  than  a  finer 
mineral  aggregate.  In  both  these  ways  the  coarse  material  is 
desirable,  but  closer  study  and  experience  has  shown  that  at  times 
it  may  be  reduced  or  largely  omitted  to  advantage,  especially  in 
damp  climates. 

To  bring  about  a  satisfactory  arrangement  of  the  first  two  points, 
or  sand  grading,  one  or  more  kinds  of  sand  are  necessary,  usually 
more  than  one.  For  example,  in  the  Fifth  Avenue  mixture  the 
main  sand  supply  was  deficient  in  100-  and  80-mesh  grains.  It 
was,  therefore,  necessary  to  add  a  certain  amount  of  fine  sand 
consisting  predominantly  of  grains  of  this  size. 

The  third  point,  and  one  also  of  great  importance,  is  that  the 
amount  of  filler  or  dust  shall  be  sufficient.  In  the  standard  mix- 
ture of  1899  this  was  intended  to  reach,  together  with  the  small 
amount  of  200-mesh  sand  and  the  natural  filler  present  in  Trinidad 
asphalt,  13  per  cent.  In  the  older,  coarse  Washington  and  St. 
Louis  mixtures  of  the  early  nineties  the  filler  and  200  sand  rarely 
reached  7  per  cent,  and  hi  St.  Louis  fell,  at  tunes,  below  3  per 
cent.  This  was  attributable  to  two  causes:  one,  the  fact  that 
such  coarse  mixtures  would  not  carry  much  dust  without  balling, 
and  the  other,  because  it  was  considered  at  that  tune  uncertain 
if  there  were  any  merit  in  using  a  filler.  We  now  know  that  dust 
gives  stability  to  the  mixture,  aids  in  excluding  water,  and  that 
the  best  surfaces  are  those  which,  up  to  a  certain  limit,  contain 
the  most  filler.  In  the  standard  mixture  of  1899  the  largest  amount 
of  dust  which  such  a  sand  grading  could  carry  was  about  13  per 
cent,  owing  to  the  relatively  small  amount  of  100  and  80  sand 
grains.  Beyond  this  percentage  the  mixtures  would  become 
greasy  or  would  ball. 

With  the  first  three  points  arranged  in  a  satisfactory  way,  the 
fourth  or  last  point  was  to  decide  on  how  much  asphalt  cement 
the  mineral  aggregate  would  carry.  This  has  been  determined 
in  recent  years  by  the  pat  test,  described  on  pages  351  and  514, 


336  THE  MODERN  ASPHALT  PAVEMENT. 

which  readily  shows  whether  an  excess  or  deficiency  in  asphalt  cement 
has  been  used.  This  test  cannot,  in  all  probability,  be  improved 
upon.  If  each  grain  of  material  in  the  mineral  aggregate  is  coated 
with  asphalt  cement  and  the  voids  more  than  filled  the  excess 
will  be  squeezed  out  hi  making  a  pat  and  stain  the  paper  exces- 
sively. If  the  voids  are  not  filled  the  only  stain  on  the  paper 
will  be  a  light  one  from  the  cement  coating  the  grains  of  sand.  A 
perfect  mixture  will  contain  just  enough  cement  to  fill  the  voids 
in  the  aggregate,  stain  the  paper  well  but  not  excessively  (Figs. 
6,  7,  8,  and  9).  The  hotter  the  mixture  the  more  liquid  the 
asphalt  cement  and  the  freer  the  stain.  Cold  mixtures  will  give 
no  indication,  while  the  difference  in  the  markings  of  a  fine  and 
coarse  sand  will  be  readily  learned  by  experience. 

The  preceding  instructions  are  satisfactory  for  turning  out 
a  mixture  for  the  conditions  ordinarily  met  with  if  the  available 
materials  admit  of  following  them,  or  for  judging  the  character 
of  old  surfaces  when  they  have  been  resolved  into  their  constitu- 
ents by  analytical  methods. 

In  cases  where  there  may  be  an  excess  of  fine  sand,  particu- 
larly of  200-mesh  material,  some  modification  of  the  method  of 
procedure  which  has  been  described  will  be  necessary.  This 
will  be  taken  up  later.1 

Work  on  the  Old  Rule-of -thumb  Basis. — In  comparison  with  a 
standard  mixture  made  according  to  the  previous  instructions 
work  done  without  any  rational  method  of  control  is  instructive. 
Several  such  mixtures  have  been  examined  which  were  laid  in 
Chicago  in  1898  and  1899  by  contractors  exercising  no  technical 
supervision  over  their  work.  See  first  table  on  page  337. 

There  is  hardly  a  mixture  among  these  that  is  not  open  to 
criticism  in  one  respect  or  another,  while  that  laid  under  the 
author's  supervision  could  in  itself  be  slightly  improved.  The 
mixtures  are  more  or  less  deficient  in  coarse  sand  as  compared 
with  the  standard  adopted.  This  is  general,  if  it  is  a  defect,  and 
is  due  to  the  character  of  the  local  sand.  The  Bermudez  mixture 
is  very  deficient  in  bitumen  and  for  no  other  reason  except  that 

1  See  page  345. 


SURFACE    MIXTURES. 


337 


enough  asphalt  cement  has  not  been  put  in.     It  would  easily 
carry  more,  as  the  sand  is  very  fine,  quite  too  much  so. 
CHICAGO,   ILL.,   MIXTURES  OF  1898   AND   1899. 


Bitu- 
men. 

Passing  Mesh 

Retained 
on  10. 

200 

100 

80 

50 

40 

30 

20 

10 

8.9 
11.2 
10.3 
8.5 
10.8 

11.1 
12.8 
13.7 
8.5 
6.2 

20.0 
8.0 
5.0 
5.0 
18.0 

35.0 
11.0 

28.0 
28.0 
26.0 

20.0 
43.0 
37.0 
41.0 
31.0 

1.0 
7.0 
4.0 
7.0 
5.0 

1.0 
4.0 
2.0 
2.0 
1.0 

1.0 
2.0 
0.0 
0.0 
1.0 

1.0 
1.0 
0.0 
0.0 
1.0 

1.0 

Trinidad  lake  asphalt.  .  .  . 
Alcatraz  asphalt 

Standard  asphalt 

Trinidad  land  asphalt..  .  . 

FOR    COMPARISON. 


Author's  supervision 


10.611.414.0 


15.o|35.o|  8.o|  3.o|  2.0    l.OJ 


The  second  mixture  is  one  which  is  hardly  open  to  serious 
comment.  The  mineral  aggregate  should  have,  however,  rather 
more  80-  and  100-mesh  grains,  so  that  they  should  together  reach 
25  to  27  per  cent. 

The  Alcatraz  has  only  6  per  cent  of  sand  coarser  than  a  50-mesh 
sieve,  and  it  is  unbalanced  in  its  80-  and  100-mesh  sizes. 

The  Standard  mixture  is  very  inferior  and  cannot  prove  sat- 
isfactory. It  is  very  deficient  in  bitumen,  dust,  and  100-mesh 
sand,  three  of  the  important  factors  hi  a  good  wearing  surface. 

The  Trinidad  land  asphalt  should  have  more  filler,  but  it  is 
not  otherwise  defective,  in  so  far  as  the  mineral  aggregate  is  con- 
cerned, except  in  the  usual  absence  of  coarse  sand. 

As  a  whole  these  mixtures  are  excellent  examples  of  ordinary 
work  done  empirically  and  without  proper  control. 

In  other  cities  even  more  glaring  defects  are  often  met,  as  can 
be  seen  from  a  few  examples: 


Cities. 

Bitu- 
men. 

Passing  Mesh 

200 

100 

80 

50 

40 

30 

20 

10 

Toronto,  Canada.  .  . 
Utica  N.  Y  

8.4* 
8.0* 
9.9 

24.6* 
26.5* 
13.1 

22.0 
31.7 
3.0* 

12.0    22.0 
17.9  !  7.7 
3.0*24.0 

5.0 
5.6 
22.0 

3.0 
1.5 
12.0 

2.0 
0.8 
7.0 

1.0 
0.3 
6.0 

Indianapolis,  Ind.  .  . 

*  The  shortcomings  are  here  marked  with  an  asterisk- 


338  THE   MODERN    ASPHALT    PAVEMENT. 

That  the  cardinal  points  in  a  mixture  were  often  neglected 
in  the  earlier  days  can  also  be  seen  from  an  examination  of  the 
materials  and  their  proportions  in  a  mixture  sent  out  on  August  8, 
1895,  for  use  on  Eighth  Avenue  in  New  York: 

SAND— COW  BAY.     (GOODWIN.) 

Passing  200-mesh  sieve Trace 

"       100-    "        " " 

"         80-   "        "   " 

"         50-    "        "   5.0% 

"         40-   "        " 13.0 

"        30-    "        "  42.0 

"        20-   "       "  37.0 

"        10-   "       "  2.0 

DUST— TUBE-MILL. 

Passing  200-mesh  sieve 66 . 0% 

"       100-   "        "  20.0 

80-   "        "  14.0 

ASPHALT  CEMENT. 
Bitumen 65.0% 

PROPORTIONS. 

Sand 801  Ibs 79.5% 

Dust 60    " 5.9 

A.  C. .  ..147    "  .  14.6 


1008  100.0 


A  mixture  made  from  the  above  materials  in  the  proportions 
given  would  have  .about  the  following  composition: 

Bitumen 9.5%        — 4th  point 

Passing  200-mesh  sieve 8.9  — 3d      " 


100- 


"  131 

80-  "    .  l.O/    2'3—lst 


50-  '  '    4.1 

"          40-  "  "    10.4 

"          30-  "  "    33. 

20-  "  «    29.6^64.8— 2d 

*          10-  "  "  . 


13. 5-| 
!9.6[64.! 
1.7J 


100.0 


SURFACE    MIXTURES.  339 

It  is  evident  that  none  of  the  four  points  in  a  good  mixture 
is  approached  in  this  one.  It  is  deficient  in  fine  sand,  far  too 
coarse,  contains  too  little  dust,  and  would  not  hold  enough  bitu- 
men. 

This  is,  of  course,  an  exaggerated  case,  but  much  mixture  of 
a  similar  description  has  been  sent  out  and  is  being  made  to-day 
by  ignorant  contractors. 

Problems  Arising  from  Lack  of  Sand  Suitable  for  Obtaining 
the  Standard  Grade. — Our  illustrations  and  experience  have  shown 
that  at  tunes  the  sands  to  be  found  in  any  locality  do  not  permit 
of  attaining  the  standard  grade  which  has  been  proposed.  For 
example,  in  Washington,  D.  C.,  there  is  no  sand  available  which 
will  supply  the  proper  amount  of  100-  and  80-mesh  material 
in  sufficient  amount.  In  other  cities  there  may  be  an  excess  of 
200-mesh  sand.  Again,  in  some  localities,  coarse  sand  is  an  expen- 
sive article,  and  it  is  impossible  to  introduce  into  the  mixture 
the  normal  amount  of  10-,  20-,  and  30-mesh  grains  at  any  reason- 
able cost.  Finally,  questions  arise  as  to  whether  under  some 
trying  conditions  a  mixture  cannot  be  made  which  is  more  resistant 
to  unfavorable  environment  than  the  standard  and  as  to  whether 
sands  of  the  same  grading  in  different  localities  the  grains  of 
which  may  have  a  different  surface  and  a  different  shape,  and  in 
consequence  of  the  last  fact  may  have  different  voids,  can  be 
handled  in  the  same  way  as  New  York  sand.  The  proper  amount 
and  the  consistency  of  the  asphalt  cement  to  be  used  under  vari- 
ous conditions  must  also  be  determined.  These  points  have 
been  so  far  settled  by  the  results  of  investigations  carried  out 
during  the  last  few  years  that  the  problems  can  now  be  discussed 
fairly  intelligently. 

Mixtures  Necessarily  Coarser  than  Standard. — The  City  of 
Washington  was  once  in  a  situation  of  this  kind.  Until  recent 
years,  there  has  been  no  available  supply  there  of  what  is  known 
as  "tempering  sand,"  and  the  surface  mixture  in  use  was  on  this 
account  deficient,  more  or  less,  in  80  and  100  mesh  grains.  In 
the  early  days  of  the  industry  this  deficiency  was  a  serious  one. 
The  average  composition  of  the  surface  mixture  laid  in  1889  was 
as  follows: 


340  THE  MODERN  ASPHALT  PAVEMENT. 

Density 2.10 

Bitumen 9.7% 

200-mesh-sieve 9.3 

100     "       "     3.0 

80     "       "     5.0 

50     "       " 20.0 

40     "       "     20.0 

30     "       "     18.0 

20     "      "     8.0 

10     "      "  7.0 


100.0 

This  mixture  is  plainly  deficient  in  80-  and  100-mesh  sand 
grains,  in  the  percentage  of  bitumen,  and  probably  in  filler  or 
actual  dust,  since  less  than  4  per  cent  of  ground  limestone,  of 
which  not  more  than  60  per  cent  passes  a  200-mesh  sieve,  was 
added  to  the  mixture,  although  the  200-mesh  material  reaches 
9.3  per  cent,  more  of  this  being  in  the  form  of  sand  grains  than  of 
dust,  a  condition  which  investigations  to  be  described  later  will 
show  has  a  decided  effect  upon  the  character  of  the  mixture. 

The  streets  on  which  the  surfaces  of  1889  were  laid  were  sub- 
jected to  very  light  travel  and  were  fairly  satisfactory  for  that 
period,  but  when  they  were  examined  in  1894  it  was  evident 
that  they  could  have  been  improved  upon  by  the  selection  of 
a  better  mineral  aggregate,  containing  more  filler,  and  which, 
consequently,  could  carry  more  bitumen. 

Of  recent  years  there  has  been  a  distinct  iimorovement 
in  the  grading  of  the  mixture  laid  in  Washington,  as  shown 
by  the  following  analysis  of  the  pavement  laid  by  the  Brennan 
Construction  Company  on  Pennsylvania  Avenue  in  1907. 

PROPORTIONS. 

Asphalt  cement  (Bermudez) 102  lbs.=  11.5% 

Limestone  dust 55   "  —     6.2 

Sand.  .  731   "  =  82.3 


888   "  =100.0% 


SURFACE    MIXTURES.  341 


ANALYSIS. 

Bitumen 10.5% 

Sand,  passing  100-mesh  sieve 25 .0 

11      retained  on  100-mesh  sieve 10.3 

"  "        "     80      "       " 12.4 

«  "        "     60      "       "      26.6 

it  a        "40"       "  23  1 

n  n        n     20     "       tf  ?.6 

In  some  other  cities  similar  conditions  are  met  with  in  regard 
to  the  available  materials  for  making  the  mineral  aggregate,  and 
experience  has  shown  that  where  the  streets  to  be  paved  are  care- 
fully drained  and  the  traffic  is  not  heavy  such  a  mixture  will  prove 
satisfactory,  although  it  is  probable  that  if  the  standard  grading 
had  been  employed  with  a  cement  which  is  somewhat  softer  than 
that  which  would  be  used  on  a  heavy-traffic  street  the  life  of  the 
pavement  would  be  somewhat  extended. 

On  the  other  hand,  it  is  the  opinion  of  certain  experts  that  a 
coarser  mixture  is  more  desirable  for  streets  of  light  traffic,  and 
that  where  the  surface  is  not  thoroughly  rolled  out  and  closed  up 
thereby  it  is  more  satisfactory  than  a  finer  one.  There  is  a  possi- 
bility that  this  may  be  so  if  the  finer  standard  mixture  is  not  made 
with  a  softer  asphalt  cement,  the  experience  of  the  author  in  1896, 
in  several  western  cities  where  streets  were  paved  having  no  traffic 
at  all,  having  shown  that  standard  surface  mixture  laid  with  a  rather 
hard  cement  cracked  to  a  very  considerable  extent  after  two  years. 
Where,  however,  a  standard  mixture  was  laid  on  such  streets  with 
a  very  soft  cement,  cracking  has  not  taken  place  under  the  same 
conditions.  For  the  reason  that  finer  sands  are  not  available  in 
Washington,  or  in  the  belief  that  a  coarser  mixture  is  more  desirable, 
the  more  recent  specifications  for  asphalt  pavements  in  that  city 
call  for  a  sand  of  the  following  grading: 

100-mesh At  least  10% 


'o 

80- and  100-mesh ...."      "     25% 

"          10-,  20-,  and  30-mesh "      "     15% 


342 


THE  MODERN  ASPHALT  PAVEMENT. 


In  view  of  the  above  facts,  where  fine  sand  is  not  to  be  pro- 
cured readily,  a  modified  standard  for  sand  grading  and  finished 
mixture  has  been  adopted. 


STANDARD  GRADING  FOR  LIGHT  TRAFFIC. 


Sand. 

Mixture. 

Bitumen 

10% 

Passing  200-mesh.  .  . 

10 

100-    "     ... 

11  |  __„ 

91  -.0 

80-    "     

ll)22% 

9/18 

60-          

33 

26 

40-          

15 

12 

30-          

13] 

101 

20- 

10  V30 

8  (-24 

"         10- 

7  1 

6  1 

100 

100 

A  very  considerable  amount  of  work  which  has  proved  entirely 
satisfactory  in  small  cities  and  towns  has  been  done  on  this  basis 
under  the  author's  supervision.  Such  mixtures  would  not,  how- 
ever, be  satisfactory  in  all  large  cities,  except  on  residence  streets, 
and  it  is  because  most  of  the  mixtures  of  the  careless  contractor 
are  never  more  satisfactory  in  their  grading  than  this  that  they 
are  not  entirely  successful  in  their  work  where  it  is  subjected  to 
heavy  traffic. 

Excess  of  Fine  Sand  of  100-  and  8o-Mesh  Size. — Where  the 
regular  sand  supplies  contain  an  excess  of  100-  and  80-mesh  material, 
and  where  it  is  impossible  to  introduce  into  the  mixture  the  normal 
amount  of  10-,  20-,  and  30-mesh  grains  at  any  reasonable  cost,  a 
new  problem  is  brought  to  our  attention.  Such  a  situation  is 
complicated  by  the  fact  that  an  excess  of  100-  and  80-mesh  grains 
may  or  may  not  be  accompanied  by  the  presence  of  a  large 
amount  of  200-mesh  material. 

If  the  200-mesh  material  is  not  present  the  mineral  aggregate 
can,  generally,  be  treated  in  much  the  same  way  as  the  standard 


SURFACE    MIXTURES.  343 

grading,  merely  allowing  for  the  fact  that  the  greater  surface  exposed 
by  the  grains  of  the  fine  material  necessitates  the  use  of  a  larger 
percentage  of  asphalt  cement.  The  resulting  mixture  may  be 
quite  satisfactory  and,  on  the  other  hand,  may  possess  less  stability 
than  it  should  and  be  more  liable  to  cracking  at  low  temperatures 
and  to  displacement.  In  other  respects  it  may  be  preferable  to 
the  standard  mixture,  if  sufficient  filler  is  used,  owing  to  the  fact 
that  the  surface  is  a  closer  one  than  when  the  coarser  particles  are 
present. 

It  may  also  be  necessary  to  use  sand  in  which,  while  the  coarser 
particles  are  present  in  nearly  normal  amount,  the  distribution  of 
the  finer  sand,  the  80-  and  100-mesh  grains,  may  be  quite  different 
from  that  found  in  the  standard  grading.  Such  a  condition  will 
necessitate  changes  in  the  handling  of  such  a  sand,  as  will  appear 
when  the  consideration  of  the  amount  of  bitumen  which  a  mineral 
aggregate  will  carry  is  arrived  at,  and  this  may  be  conveniently 
taken  up  at  this  point. 

The  standard  New  York  sand  without  200-mesh  material  or 
filler  should  contain  17  per  cent  of  grains  passing  the  100-mesh 
and  17  per  cent  passing  the  80-mesh  screen,  resulting  in  the  pres- 
ence of  only  13  per  cent  of  each  of  these  grades  in  the  finished 
mixture.  For  the  purpose  of  studying  the  effect  of  an  alteration  of 
the  proportions  of  these  two  sands  some  sands  have  been  made  up 
on  an  experimental  basis  and  the  voids,  weight  per  cubic  foot,  with, 
and  without  filler,  determined.  See  results  tabulated  on  page  344, 

In  the  sand,  both  with  and  without  filler,  No.  1,  the  lack  of  100- 
mesh  grains  and  increase  of  80  above  the  usual  proportion  causes 
an  increase  in  the  voids  over  those  found  in  the  standard  New 
York  grading.  An  increase  in  both  80-  and  100-mesh  grains 
to  5  and  6  per  cent  each  above  the  normal,  No.  5,  reduces  the 
voids  decidedly  with  the  plain  sand  and  slightly  when  filler  is  present, 
but  with  all  the  other  arrangements,  while  the  sands  alone  may 
be  improved,  there  are  larger  voids  when  the  filler  is  present  than 
in  the  normal  mixture.  It  seems,  therefore,  that  unequal  amounts 
of  80-  and  100-mesh  are  not  desirable,  but  that  perhaps  larger 
amounts  of  both  might  be,  since  the  voids,  when  45  per  cent  of 
the  two  sands  are  present  instead  of  34  per  cent,  are  reduced 


344 


THE  MODERN  ASPHALT  PAVEMENT. 


WEIGHT  PER  CUBIC  FOOT  AND  VOIDS  IN  NEW  YORK  SANDr 
WITH  VARYING  PERCENTAGES  OF  100-  AND  80-MESH 
MATERIAL. 


1 

2 

3 

4 

5 

N.  Y. 

Regular 
Grading 
with  same 
Sand. 

Passing  100-mesh  sieve 

4% 

30% 

28% 

17% 

22% 

17% 

<  <         SO-    '  '        '  * 

30 

4 

17 

28 

23 

17 

"         50-    "        " 

31 

31 

26 

26 

26 

30 

a         40_    «        u 

16 

16 

13 

13 

13 

13 

"         30-    "        " 

8 

8 

7 

7 

7 

10 

<i         20-    "        " 

7 

7 

6 

6 

6 

8 

tt         1Q,    «        « 

4 

4 

3 

3 

3 

5 

100 

100 

100 

100 

100 

100 

Per  cent  100-mesh  grains. 
«       «       on      '(          ft 

Low 
High 

High 
Low 

High 
Normal 

Normal 
High 

High 
High 

Normal 
Normal 

Weight    per   cubic   foot 
with  no  200  

108.3 

110.0 

110.0 

111.5 

112.5 

109.9 

Voids.            

35.1 

34.1 

34.1 

33.2 

32.8 

34.2 

Weight    per   cubic   foot 
with  13  per  cent  dust  .  . 

119.4 

119.6 

118.9 

119.0 

121.7 

120.4 

Voids.            

28.5 

28.3 

28.8 

28.7 

27.1 

27.8 

slightly.  The  presence  of  so  much  fine  material,  however,  it  is 
feared,  would  make  the  mixture  mushy,  and  in  addition  it  is  generally 
very  difficult  and  expensive  to  accomplish  this,  since  such  material 
is  not  always  available.  More  asphalt  cement  is  also  necessary  to 
cover  the  fine  grains,  which  makes  the  mixture  more  expensive, 
without  an  adequate  return. 

The  effect  of  such  changes  in  the  standard  grading  upon  the 
percentage  of  bitumen  which  the  mixture  will  carry  is  well  illustrated 
by  the  analyses  of  the  following  mixtures  which  were  turned  out 
in  New  York  under  the  author's  supervisions  in  1899.  See  table  on 
page  345. 

It  must  be  added,  however,  that  some  of  the  difference  in 
the  percentage  of  bitumen  in  these  cases  may  be  due  to  a  variation 
in  the  shape  or  surface  of  the  sand  grains  as  well  as  to  the  grading, 
and  that  similar  results  might  not  be  obtained  with  the  same 
grading  for  sands  from  other  localities. 


SURFACE    MIXTURES. 


345 


NEW  YORK  MIXTURE— PAT  PAPERS  ALL  WELL  STAINED. 


• 

Standard 
Average. 

A 

B 

C 

D 
Av.  N.  Y. 

Week 
Ending 

Date     .     ... 

\.Y    '99 

2_7-'00 

9-20-'  99 

2-28-'00 

8-26-?99 

Proportions  : 

Sand  

790 

775 

765 

Dust  

85 

100 

110 

Asphalt  cement  

149 

95  (Ber.) 

167 

Remarks: 

Per  cent  of  100-mesh  grains 

«         ft       «      Cf)_      •  •              •  • 

Normal 
Normal 

Low 
High 

Normal 
Low 

High 
Normal 

Normal 
High 

Passing  100-mesh  sieve  

17% 

12% 

19% 

28% 

16% 

"         80-                    

17 

24 

9 

16 

23 

50-                    

31 

37 

28 

37 

38 

"         40- 

16 

15 

20 

12 

12 

"         30- 

8 

5 

12 

3 

5 

"         20- 

7 

4 

7 

3 

4 

10-    "             

4 

3 

5 

1 

9 

100 

100 

100 

100 

100 

Bitumen 

10  5°^ 

9  5<7r 

9  5°^ 

11  3°v 

10  4°n 

Dust  and  sand  (passing  200 

sieve) 

13  0 

15  5 

15  5 

14  7 

1°  1 

Sand.  . 

76  5 

75  0 

75  0 

74  0 

77  5 

100.0 

100.0 

100.0 

100.0 

100.0 

Effect  of  2oo-Mesh  Material. — In  the  case  of  sands  which  con- 
tain a  very  considerable  amount  of  material  passing  the  200-mesh 
sieve  the  conditions  will  be  found  to  be  different  from  any  of  those 
which  have  been  previously  discussed.  That  portion  of  the  sand 
which  will  pass  a  200-mesh  sieve  may  consist,  as  has  been  previously 
shown  in  considering  pulverized  mineral  matter  for  use  as  a  filler, 
of  particles  resembling  sand  and  of  more  impalpable  material, 
which  may  be  considered  as  true  dust  or  filler.  The  effect  of  a 
large  proportion  of  200-mesh  grains  in  the  sand  on  the  surface 
mixture  will  depend  largely,  therefore,  on  whether  they  are  sandy 
or  fine  enough  to  act  as  a  filler,  and  also  largely  on  the  character 
of  the  sandy  grains  themselves,  that  is  to  say,  their  shape  and 
surface.  If  the  coarser  200-mesh  grains  are  round  a  mixture  con- 


346  THE  MODERN  ASPHALT  PAVEMENT. 

taining  any  considerable  amount  of  them,  especially  if  the  remainder 
of  the  sand  is  largely  of  100-  and  80-mesh  size,  will  be  very  mushy 
and  readily  displaced.  In  1901,  in  Kansas  City,  Mo.,  a  mixture 
was  turned  out  the  sand  of  which  contained  as  much  as  14  per  cent 
of  sandy  grains  of  200-mesh  size.  With  10  per  cent  of  filler  the 
resulting  mixture  was  very  mushy  and  marked  badly  on  the  street, 
although  it  showed  by  analysis  over  19  per  cent  of  200-mesh  material 
and  consequently  might  be  supposed  to  be  a  stable  mixture.  An 
increase  of  the  filler  to  12  per  cent  improved  the  general  character 
of  the  mixture  very  much,  but  it  was  never  satisfactory  and  the 
use  of  this  sand  was  abandoned,  although  it  was  at  first  hoped  that 
such  a  fine  mixture,  giving  an  extremely  close  surface,  might  be 
more  satisfactory  than  the  coarser  standard  mixture. 

On  the  other  hand,  in  Toronto,  Ont.,  and  in  Rochester,  N.  Y., 
where  the  sands  at  the  same  time  contained  23  and  20  per  cent, 
respectively,  of  200-mesh  material,  the  amount  of  filler  could  not 
be  carried  beyond  4  per  cent,  as  a  larger  quantity  made  both  mix- 
tures very  bally  and  impossible  to  roll  and  rake  on  the  street.  In 
these  cases  the  200-mesh  material  apparently  acted  in  itself  largely 
as  a  filler.  At  other  points  loamy  sands  have  been  found  the 
loam  in  which,  when  it  does  not  bake  into  balls  on  being  heated 
in  the  sand-drums,  proves  to  be  a  satisfactory  filler. 

The  character  of  a  200-mesh  .material  in  any  sand  cannot  be 
determined  by  the  use  of  sieves,  as  nothing  finer  than  the  200-mesh 
sieve  is  available  and  this  will  not  differentiate  between  sand 
grains  of  200-mesh  size  and  the  impalpable  powder  which  acts 
as  a  filler,  but  this  may  be  done  by  elutriating  the  material  by 
the  method  described  elsewhere.  In  the  sands  in  use  in  New 
York,  especially  in  that  from  Cow  Bay  on  Long  Island,  consider- 
able extremely  fine  material  is  found,  this  amounting  at  times 
to  10  per  cent  or  more  passing  a  200-mesh  sieve.  On  separation 
of  this  material  and  elutriation  it  was  found  that  between  50  and 
60  per  cent  of  it  would  at  times  be  in  the  nature  of  a  filler  and 
at  others  not  more  than  30  per  cent.  In  a  case  where  the  pro- 
portion of  sand  and  filler  were  about  the  same  it  was  found  that  the 
mineral  aggregate  would  still  carry  a  very  considerable  further 
proportion  of  filler  and  that  the  grading  must  be  regarded  as 


SURFACE    MIXTURES. 


347 


being  extended  in  the  fine  direction  as  if  there  were  a  possibility 
of  differentiating  the  material  with  finer  sieves  than  are  available. 
Such  a  mineral  aggregate  would  carry  between  11  and  12  per 
cent  of  bitumen,  frequently  approaching  the  latter.  As  will  be 
seen  when  considering  the  grading  of  a  coarse  asphaltic  concrete, 
in  such  a  material  the  percentage  of  bitumen  is  much  reduced  by 
the  addition  of  the  larger  particles,  and  it  may,  therefore,  be 
assumed  that  on  either  side  of  our  standard  grading  we  may  place 
other  gradings  according  to  the  following  scheme.  It  is,  of  course, 
to  be  understood  that  with  very  fine  grains  a  certain  amount  of 
fine  filler  would  be  present,  although  theoretically  absent,  while 
the  same  would  hold  in  regard  to  fine  material  with  coarser 
mixture. 


Sieves. 

Stand. 
Mix. 

Bitumen 

14 

10  5 

8  0 

600      .... 

13 

500     

13 

13 

400    

13 

13 

13 

300  

24 

13 

13 

13 

200 

11 

24 

13 

13 

13 

100  
80  
50      .  . 

8 
5 
3 

11 
8 
5 

24 
11 

8 

13 
24 
11 

13 
13 
24 

13 
13 
13 

13 
13 

13 

40  
30     

0 

3 
0 

5 
3 

8 
5 

11 

8 

24 
11 

13 
24 

13 
13 

13 
13 

13 

20    

0 

3 

5 

8 

11 

24 

13 

13 

10 

0 

3 

5 

8 

11 

24 

13 

5 

0 

3 

5 

8 

11 

24 

3 

0 

3 

5 

8 

11 

2 

0 

3 

5 

8 

1 

0 

3 

5 

I 

0 

3 

The  above  diagram  shows  that,  theoretically,  the  standard 
can  be  pushed  up  and  down,  according  to  the  amount  of  fine  and 
coarse  material  which  is  present,  and  that  at  the  same  time  it 
will  be  found  that  the  amount  of  bitumen  which  the  mineral 
aggregate  will  carry  will  change  to  a  marked  degree.  This  may 
be  illustrated  by  the  following  mixtures: 


348 


THE  MODERN  ASPHALT  PAVEMENT. 


New  York, 
1904. 

Chicago, 
1901. 

Boston, 
1901. 

Newark, 
1901. 

Biti 
Pas 

imen 

12.0% 
19.0 

io.o\1Q 

9.0/1 
26.0 
12.0 
6.0] 
4.0^  12 
2.0J 

11.4% 

18.6 
33.014? 
14.  0/47 
18.0 
2.0 
1.0] 
1.0*    3 
l.Oj 

10.7% 
14.3 
12.01™ 
12.0  J24 
26.0 
10.0 
7.0] 
5.0  [  15 
3.0J 

9.6% 
9.4 

ii.o\17 

6.0/17 
18.0 
16.0 
12.0] 
9.0  1-30 
9.0J 

sing  200-mt 
100- 
80- 
50- 
40- 
30- 
2C- 
10- 

;sh  sie 

ve.  .  . 





100.0 

100.0 

100.0 

100.0 

ASPHALTIC  CONCRETES. 


Barber  Asphalt 
Paving  Co., 
New  York. 

Warren  Bros., 
St.  Louis,  Mo. 

Bitumen 

6  2% 

3  4%  1 

Filler  . 

7  8 

2  9 

Sand.  . 

29  0 

12  0 

Stone  passing  \"  screen.  .  .  . 

18.0] 

4.2] 

21.0^57 
18.  Oj 

6.6lgl  - 
55.6    81'7 

'  '      retained  on  1"  screen  . 

-    

15.  3J 

100.0 

100.0 

1  Coal-tar  soluble  in  CSz. 

It  is  very  evident  from  the  preceding  that  the  grading  of  a 
mineral  aggregate  has  a  very  large  bearing  on  the  amount  of  bitu- 
men that  it  can  carry,  and  it  may  be  stated  as  a  general  rule  that : 

1.  If  the  sand  is  finer  than  the  standard,  increase  the  filler 
and  the  asphalt  cement. 

2.  If  the  sand  becomes  coarse,  reduce  the  filler  and  the  asphalt 
cement. 

3.  If  the  200-mesh  material  in   the   sand  is  high,  determine 
whether  it  is  sand  or  a  filler.     If  it  is  a  sand,  and  cannot  be  avoided 
by  the  use  of  sand  from  some  other  source,  and  if  it  acts  badly 
in  the  mixture,  get  rid  of  it  if  possible  by  means  of  blowing  it 
out  with  a  forced  draft  or  suction,  or  add  more  filler  and  more 
asphalt  cement  if  this  is  impossible.     If  a  portion  of  it  is  of  the 
nature  of  a  filler  allow  for   this  in  the   amount  of  filler  that  is 


SURFACE    MIXTURES. 


349 


added.  If  the  only  available  sand  contains  200-mesh  grains, 
which  make  a  mushy  mixture,  remedy  this  by  the  addition  of 
more  filler  if  possible.  In  some  cases  the  200-mesh  sand  will  give 
a  mushy  mixture  under  all  circumstances  and  in  this  case  every 
effort  should  be  made  to  do  away  with  the  use  of  such  material, 
or  to  remove  the  defect  by  mixing  it  with  some  other  sand  supply. 
Examples  of  the  percentage  of  200-mesh  material  which  is 
so  fine  as  to  act  as  a  filler,  since  it  does  not  settle  in  water  in  15 
seconds,  is  shown  for  the  sands  of  various  cities  in  the  following 
table: 

ELUTRIATION  OF  200-MESH  MATERIAL  FROM  PLATFORM  SAND 


Test  number 

71714 

Kansas  City, 
Mo. 

3% 
17.2% 

55560 

Chicago, 
111. 
6% 
10.9% 

56372 

Toronto, 
Ont. 

23% 
8.6% 

City                                   .    ... 

Material  passing  200-mesh.  .  . 
Acting  as  filler  

74814 

Ottawa, 
Ont. 

13% 

27% 

73176 

Seattle, 
Wash. 

10% 
46.4% 

72355 

Buffalo, 
N.Y. 

12% 
43.2% 

73420 

Long  Isl- 
and City, 
N.Y. 

18% 
54.3% 

City.  . 

Material  passing  200-mesh  .  .  . 
Acting  as  filler  

Examples  of  very  mushy  mixtures  have  not  been  infrequent 
in  the  West.  Some  years  ago  a  mixture  was  turned  out  in  Louis- 
ville, Ky.,  having  the  following  composition: 


Bitumen 11-7% 

Passing  200-mesh 17.3 

"       100- 
tt 

tt 
tt 


80- 
50- 
40- 
30- 
20- 
10- 


to}" 

9.0 
9.0 
1.0i 
l.Oj   3 

l.OJ 


39.0 
19.0 


100.0 


550 


THE  MODERN  ASPHALT  PAVEMENT. 


In  this  mixture  about  10  per  cent  of  dust  was  being  used  before 
it  was  brought  to  the  attention  of  the  author.  On  examination 
it  was  found  that  the  sand  was  deficient  in  100-  and  80-mesh 
grains  and  contained  from  5  to  7  per  cent  of  loam  acting  as  a  filler. 
The  reduction  of  the  dust  to  4  per  cent  changed  its  character  so 
much  that  it  was  no  longer  mushy.  The  modified  surface  has 
proved  entirely  satisfactory. 

In  the  early  days  of  the  industry  much  difficulty  was  met 
with,  as  has  been  mentioned  in  discussing  the  nature  of  sands, 
in  turning  out  a  satisfactory  mixture  in  two  western  cities  where 
river  sands  were  in  use.  In  both  cases  this  was  only  overcome 
by  the  entire  abandonment  of  the  supplies  in  use  and  the  selection 
of  others.  With  the  old  supplies  the  mineral  aggregate  would 
not  carry  ten  per  cent  of  bitumen  and  the  amount  varied  with 
different  deliveries  of  sand.  In  another  city  the  mineral  aggre- 
gate, while  well  graded,  carried  too  little  bitumen  to  permit  the 
finished  surface  from  responding  to  the  great  contraction,  due 
to  sudden  drops  of  temperature,  with  the  result  that  all  the  pave- 
ments in  this  city  were  a  mass  of  cracks.  With  the  selection  of 
other  sand  supplies  this  has  been  overcome,  and  mixtures  having 
the  following  composition  have  been  produced: 


City 

Mo.  1. 

City 

No.  2, 

1896. 

1904. 

1896. 

1901. 

9  9% 

11    3% 

9   4% 

10  6% 

Passing  200-mesh  .  . 

14  1 

15  7 

9  5 

114 

"        100-    " 

9  0 

15  0 

11  0 

1  1    0 

"         80-    " 

13  0 

14  0 

18  0 

170 

"         50-    "    

33  0 

27  0 

26  0 

30  0 

"         40-    "    

11.0 

6  0 

11  0 

10  0 

"         30-    "    

6  0 

5  0 

9  0 

6  0 

"         20-    "    

3  0 

4  0 

4  0 

3  0 

"         10-    "    

1  0 

2  0 

2  0 

1  0 

100.0 

100.0 

100.0 

100.0 

Here  the  difficulty  lay  in  the  fact  that  the  sand  first  in  use 
was  composed  of  grains  which  had  a  surface  of  such  a  nature  that  a 
thick  coating  of  asphalt  cement  would  not  adhere  to  them. 


SURFACE    MIXTURES.  351 

The  Amount  of  Asphalt  Cement  or  Bitumen  which  a  Mineral 
Aggregate  Will  Carry. — It  has  become  very  evident  from  what  has 
been  said  in  the  preceding  pages  that  the  amount  of  bitumen  or 
asphalt  cement  in  any  mixture  is  very  variable,  depending  upon  the 
grading  of  the  mineral  aggregate  and  upon  the  peculiar  surface  of 
the  sand  grains.  It  is  a  self-evident  fact  that  this  amount  in  any 
mixture  should  be  sufficient  to  thickly  coat  every  particle  of  mineral 
matter  and  fill  the  voids  in  the  sand,  if  the  latter  are  sufficiently 
small,  in  the  actual  size  of  the  spaces  between  the  grains  but  not 
in  volume,  to  permit  of  doing  so  without  making  the  resulting 
asphalt  surfaces  too  susceptible  to  temperature  changes.  With 
too  much  bitumen  the  sand  grains  composing  the  mineral  aggregate 
are  readily  displaced  among  themselves,  especially  in  the  absence 
of  a  sufficient  amount  of  filler,  and  the  surface  is  not  stable  and 
will  mark  badly  and  push  out  of  shape.  With  too  little  bitumen 
the  surface  cracks,  owing  to  its  inability  to  withstand  sudden 
changes  in  temperature,  and  also  becomes  displaced  because  it  is 
not  a  solid  mass.  Mr.  Dow's  illustration,  which  compares  an  asphalt 
pavement  to  a  seabeach  at  different  states  of  the  tide,  is  an  excellent 
one.  Beach  sand  with  the  voids  just  rilled  with  water,  as  the 
tide  goes  out,  is  firm  and  stable.  A  horse  hardly  marks  it.  When 
it  begins  to  dry  out  it  is  loose  and  is  readily  displaced.  When  it  is 
supersaturated  with  water  it  is  a  quicksand. 

The  proper  amount  of  bitumen  for  various  mineral  aggregates 
in' common  use  may  vary  from  9  to  over  14  per  cent.  As  examples 
sands  found  and  in  use  in  Moline,  HI.,  in  1902,  would  carry  but  8.5 
per  cent  of  bitumen,  while  in  Paris,  France,  and  London,  England, 
11.5  per  cent  could  be  used,  and  in  Glasgow,  Scotland,  and  Seattle, 
Wash.,  over  12.5  per  cent,  as  shown  by  the  following  analyses.  See 
table  on  page  352. 

If  a  strict  interpretation  of  the  instructions  is  followed  and  only 
10.5  per  cent  of  bitumen  is  introduced  the  mixture  with  such  sand 
will,  of  course,  be  unsatisfactory,  and  such  difficulties  have  been 
frequently  met  with  owing  to  lack  of  judgment  on  the  part  of 
yard  foremen  and  superintendents. 

The  actual  amount  to  be  used  in  any  case  must  be  determined 
by  the  pat-paper  test  described  on  page  514.  This  test,  however, 


352 


THE  MODERN  ASPHALT  PAVEMENT. 


is  deceptive  unless  the  mixture  is  at  a  temperature  where  the  asphalt 
cement  is  quite  liquid.  With  cold  mixtures  the  test  is  of  no  value, 
while  excessively  hot  ones  may  stain  the  paper  too  freely. 


Citv  . 

Moline 

Paris 

London 

Glasgow 

Seattle 

Bitumen  soluble  in  CS2  
Passing  200-mesh  sieve  .  . 

8.4% 
15  6 

11.2% 
14  7 

11.1% 
15  3 

12.0% 
18  0 

12.3% 
12  7 

"       100-             " 

14  0 

18  7 

12  7 

15  0 

11.0 

"         80-             "... 

4  0 

23  1 

20  5 

25  0 

9.0 

"         50-             "    ... 

16.0 

26  3 

33  7 

24  0 

23.0 

40-             "    
"         30-             "    
"         20-    "        " 
"         10-    "        "    

17.0 
13.0 
9.0 
3.0 

3.9 
1.6 
.4 
.1 

3.6 
1.5 
1.1 
.5 

4.0 
2.0 
0.0 
0.0 

15.0 
10.0 
5.0 
2.0 

iOO.O 

100.0 

100.0 

100.0 

100.0 

Characteristic  pat  papers  are  illustrated  on  the  following  sheets. 

The  paper,  Fig.  6,  illustrates  a  light  stain  made  by  a  mixture 
which,  although  of  a  proper  temperature,  is  deficient  in  bitumen. 
The  paper  reproduced  in  Fig.  7  illustrates  a  medium  stain, 
showing  a  slight  deficiency  in  bitumen.  The  paper  reproduced 
in  Fig.  8  shows  a  strong  stain  produced  by  a  standard  mixture 
carrying  a  suitable  amount  of  bitumen.  The  paper  reproduced 
in  Fig.  9  represents  a  heavy  stain,  pointing  to  the  presence  of 
an  excess  of  bitumen  if  the  temperature  of  the  latter  is  not  abnor* 
mally  high. 

Coarse  sands  such  as  are  found  in  abnormal  mineral  aggregates 
give  a  rather  different  stain.  Experience  will  prove  the  best 
means  of  interpreting  the  test.  It  is  a  very  valuable  one  with 
Trinidad  lake  asphalt  mixture,  but  less  so  with  others,  as  other 
bitumens  are  more  susceptible  to  temperature  changes. 

In  making  a  pat  test  the  appearance  of  the  surface  of  the  ho<* 
pat  is  quite  as  instructive  as  that  of  the  stain  upon  the  paper, 
since  if  the  mixture  is  unbalanced  in  any  way  greasiness  is  often 
visible,  which  should  be  removed  by  the  adjustment  of  sand,  filler, 
and  bitumen,  which  can  only  be  accomplished  by  experiment, 
the  reduction  of  the  amount  of  filler  accomplishing  this  at  one 
time  and  increasing  it  at  another. 


FIG.  6.— Light  Stain. 


353 


FIG.  7. — Medium  Stain. 


354 


FIG.  S. — Strong  Stain. 


355 


FIG.  9. — Heavy  Stain. 


356 


SURFACE   MIXTURES. 


35" 


Reasons  for  the  Necessity  for  a  Larger  Percentage  of  Bitumen 
in  a  Fine  than  in  a  Coarse  Mixture. — It  has  already  been  mentioned 
that  one  reason  why  the  finer  mixture  requires  a  larger  percentage 
of  bitumen  than  the  coarser  one  is  that  the  extent  of  surface  of 
the  sand  grains  to  be  covered  with  bitumen  is  much  larger  in  the 
former  than  in  the  latter  case. 

The  number  of  particles  in  a  gram  of  grains  of  uniform  diameter 
and  of  different  sizes  and  the  square  centimeters  of  surface  exposed 
by  one  gram  of  such  grains  are  presented  in  the  following  tables. 

These  figures  are  obtained  by  means  of  the  following  formulas: 


and 


surf  ace =x(d)2n, 


where  a  is  the  weight  of  the  particles,  in  this  case  one  gram,  d  the 
diameter  of  the  particles,  aj  the  specific  gravity  of  them,  and  where 
n  is  the  number  of  particles. 

Where  the  diameter,  d,  is  given  in  centimeters  and  a  in  grams, 
the  following  constants  are  useful: 

LOGARITHMS  OF  CONSTANTS  IN  CENTIMETERS. 


Vlesb,  Sieve 

*d)*» 

log  ic(d)*n. 

6 

10 

.150 

6.6705180 

8.8493321 

20 

.084 

6.9150320 

8.3457081 

30 

.058 

6.4325281 

8.0240055 

40 

.040 

5.9484241 

7.7012695 

50 

.026 

5.3871640 

7.3270961 

80 

.020 

5.0453441 

7.0992095 

100 

.013 

4.4840743 

6  .  7250363 

200 

.008 

3.6515141 

6.3033295 

1  minute 

.005 

3.2491541 

5.8949895 

30  minutes 

.0025 

2.3360641 

5.2930295 

2  hours 

.00075 

0.7674280 

4.2472721 

16      " 

.00025 

0.3360641 

3.2930295 

log  ^-  =  .  1422441. 


358 


THE  MODERN  ASPHALT  PAVEMENT. 


ONE  GRAM  OF  SAND  OF  UNIFORM  SIZE  CONTAINS. 


Mesh  Sieve. 

Millimeter. 

Particles. 

Square 
Centimeters. 

10 

1.50 

212.8 

15.0 

20 

.84 

1,215.9 

27.0 

30 

.58 

3.693.6 

39.4 

40 

.40 

11,261.0 

56.6 

50 

.26 

41,005.0 

87.1 

80 

.20 

90,066.0 

113.2 

100 

.13 

328,032.0 

174.2 

200 

.08 

1,407,620.0 

283.0 

1  minute 

.05 

5,643,700.0 

442.4 

30  minutes 

.025 

46,124,900.0 

905.7 

2  hours 

.0075 

6,800,990,000.0 

1,201.6 

16      " 

.0025 

46,124,900,000.0 

9,056.6 

1  gram  to  1  Ib.  X 453.59,  log.  2.6566654  for  particles. 
Sq.  cm.  to  sq.  ft.,  divide  by  2.9680569  for  surface. 


Where  it  is  desired  to  determine  the  number  of  particles  and 
the  surface  exposed  by  grains  of  different  sizes  which  go  to  make 
up  an  aggregate  of  definite  weight,  the  preceding  formulas  become: 


where  a  is  the  weight  of  each  group  of  particles  and  A  the  total 
weight  of  the  material,  in  the  following  case  one  pound.  Using 
this,  the  number  of  particles  and  the  square  feet  of  surface  in  one 
pound  of  the  mineral  aggregates  in  New  York  mixtures  of  1895 
and  1898  are  found  to  be  as  follows.  See  tables  on  page  359. 

It  appears  that  the  finer  aggregate  presents  a  surface  of 
60.5  square  feet  to  the  pound,  the  coarser  only  44.4,  or  39,407  and 
52,093  square  feet  per  9  cubic  foot  box  respectively;  that  is  to 
say,  the  finer  has  one- third  more  surface,  and  as  this  must  be  covered, 
more  asphalt  will  be  required  for  the  finer  than  the  coarse  aggre- 
gate. This  explains  why  the  addition  of  dust  will  always  increase 
the  amount  of  asphalt  cement  which  a  mixture  will  hold,  although 
the  voids  may  be  reduced,  as  a  pound  of  the  best  Long  Island 


SURFACE   MIXTURES. 


359 


NUMBER   OF   PARTICLES   AND   THEIR  SQUARE   FEET  OP 

SURFACE  IN  ONE  POUND  OF  SAND  AND  DUST. 

NEW  YORK  MIXTURE,  1895. 


Mesh  Sieve. 

Per  Cent. 

Particles. 

Square  Feet 
of  Surface. 

10 

13 

12,592 

.958 

20 

12 

66,186 

1.579 

30 

10 

167,547 

1.901 

40 

13 

664,250 

3.593 

50 

27 

5,021,870 

11.479 

80 

10 

4,086,220 

5.527 

100 

7 

10,415,700 

5.952 

200 

5 

31,924,300 

6.909 

.005  mm. 

3 

76,671,400 

6.480 

100 

129,030,065 

44.378 

One  box  of  mixture  (average  888  Ibs.),  39,407.664 
NEW  YORK  MIXTURE,  1898. 


10 

4 

3,674 

.295 

20 

7 

38,808 

.921 

30 

9 

150,796 

1.715 

40 

11 

561,866 

3.033 

50 

26 

4,835,870 

11.054 

80 

15 

6,127,910 

8.099 

100 

15 

22,319,400 

12.754 

200 

7 

44,694,000 

9.672 

.005mm. 

6 

153,343,000 

12.960 

100 

232,075,324 

60.503 

One  box  of  mixture  (average  861  Ibs.),  52,093.083 

City  dust  with  the  following  siftings  will  contain  the  number  of 
particles  and  the  surface  in  square  feet  given  below : 


Size  Particles, 
Centimeters. 

Per  Cent. 

Number  of  Particles. 

Square  Feet 
of 
Surface. 

.008 
.005 

.0025 
.00075 
.00025 

18.8 
17.7 
51.3 
5.0 
7.2 

120,035,300 
452,360,200 
10,732,9-50,000 
30,775,730,000 
150,634,400,000 

25.976 
38.231 
226.825 
58.590 
178.199 

100.0 

192,715,475,500 

527.821 

or  if  all  of  t 
.0025  cm. 

ie  dust  is  of 
n  diameter: 

20,922,050,000 

442.157 

360  THE  MODERN  ASPHALT  PAVEMENT. 

This  enormous  area  of  surface  allows  the  presence  of  a  larger 
quantity  of  bitumen  in  a  fine  mixture  than  in  a  coarse  one.  The 
question  of  the  thickness  of  the  film  of  the  melted  asphalt  cement 
on  the  extended  surface  of  the  sand  grains  is  one  which,  from 
the  elaborate  studies  of  soil  physics,  it  is  plain  must  be  of  great 
importance  in  regulating  the  amount  of  bitumen  which  different 
sands  will  require  to  prevent  porosity  and  instabilty  in  the  mix- 
ture. Much  pertinent  information  on  this  point  will  be  found 
in  Whitney's  Bulletins,  Weather  Bureau,  Division  of  Soils,  U.  S. 
Department  of  Agriculture,  and  Wiley's  Principles  of  Agricultural 
Analysis,  but  our  understanding  of  the  question  at  present  is 
insufficient  to  permit  of  going  into  the  matter  at  this  time.  It 
will  be  investigated  in  the  future. 

In  this  connection  some  recent  determinations  by  Messrs. 
Briggs  and  McCall,  of  the  Bureau  of  Soils,  U.  S.  Department  of  Agri- 
culture, "  On  the  Thickness  of  Adsorbed  Aqueous  Films,"  are  of 
interest.  They  found  the  following  values  for  several  materials: 

Silica 167.00X10-'  cm. 

Glass 18.00X10-6     " 

Quartz 45X10~8     " 

The  application  of  these  data  to  an  asphalt  surface  lies  in 
the  fact  that  sand  may  consist  of  particles  which  may  vary  as 
largely  in  the  thickness  of  the  film  of  asphalt  which  will  adhere 
to  them  as  the  materials  experimented  with  above,  and  this  may 
explain  why  one  sand  with  the  same  grading  and  voids  as  another 
may  hold  different  percentages  of  bitumen. 

The  New  York  mixture  is  desirable  in  so  far  as  it  will  usually 
carry  10.5  to  11.5  per  cent  of  bitumen,  when  the  grains  are  all 
coated  and  the  voids  filled,  as  shown  by  the  paper  pat  test,  and 
this  affords  a  sufficient  amount  to  keep  out  water  and  provide 
for  the  contraction  due  to  a  rapid  fall  in  temperature. 

With  the  low  voids  it  might  at  first  be  assumed  that  such  $  mix- 
ture would  hold  less  asphalt  than  one  with  a  greater  volume,  but 
it  has  already  been  shown  that  the  low  voids,  when  accompanied 
by  plenty  of  fine  sand,  do  not  have  this  effect,  as  the  adsorbed 
bitumen,  or  that  necessary  as  a  paint  coat  to  cover  the  more  numer- 


SURFACE   MIXTURES. 


361 


ous  small  grains,  is  something  to  be  considered  beyond  that  necessary 
to  fill  the  voids.  On  the  contrary,  a  well-graded  fine  mixture 
with  small  voids  will  often  carry  more  bitumen  than  a  coarse 
one  with  larger  voids. 

Comparison  of  the  Characteristics  of  Different  Sands  Having 
the  Same  Sand  Grading. — If  the  sand  used  in  New  York,  arranged 
according  to  the  grading  in  the  mixture  laid  in  that  city  in  1898 
and  1899,  is  to  be  regarded  as  most  satisfactory,  as  shown  in  the 
following  figures,  it  must  be  by  no  means  assumed  that  on 
that  account  the  New  York  sand  is  the  best  sand;  that  is  to 
say,  consists  of  the  best  shaped  grains  or  of  those  having  the 
best  surface  to  afford  a  proper  adhesion  of  the  asphalt  cement 
and  allow  of  a  sufficiently  thick  coating.  As  a  matter  of  fact 
the  contrary  is  the  case.  It  is  possible  that  with  other  sands 
accommodated  to  the  New  York  grading  even  better  results  could 
be  obtained  than  with  the  New  York  sands  themselves. 


1898. 

1899. 

Bitum 
Passin 

tt 
tt 
tt 
tt 
tt 
tt 

»n  

10.5% 
13.7 
13.1 
13.4 
22.6 
10.0 
7.6 
5.6 
3.5 

10.5% 
13.0 
12.7 
12.6 
23.9 
12.1 
6.6 
5.3 
3.3 

T  ^00-mesli  sieve  •  • 

3  100-    "        " 

80-    "        "    . 

50-    "        "    .    . 

40-    "        "    

30-    "        "    

20-    "        "    
10-    "        "    

100.0 

100.0 

Experiments  have  been  undertaken  and  completed  for  determin- 
ing what  the  differences  are  in  this  respect  in  the  available  sands 
in  different  cities  of  the  country. 

It  has  been  shown  that  the  grading  of  the  New  York  mineral 
aggregate  is  such  that  the  New  York  mixture  is  the  densest  of  any 
satisfactory  one  in  the  country,  and  it  appears  that  in  the  case  of 
the  sand  of  every  other  city  hi  the  country,  when  the  grading 
according  to  which  it  was  used  some  years  ago  is  changed  to  that 
of  the  New  York  mineral  aggregate  of  to-day  (1899),  the  density 


362 


/HE  MODERN  ASPHALT  PAVEMENT. 


of  the  resulting  mixture  is  increased  with  one  or  two  exceptions, 
and  in  the  same  way  if  the  New  York  aggregate  is  changed  from 
its  own  grading  to  those  of  other  cities  its  density  is  decreased. 

The  grading  of  the  local  sands  with  and  without  dust,  the  voids 
and  the  weight  per  cubic  foot  of  each  on  its  own  grading,  on  the 
grading  of  the  New  York  sand  and  aggregate  and  of  the  New  York 
sand  on  the  local  grading  as  determined  in  1900  are  given  in  the 
following  tables: 
GRADING  OF  SANDS  IN  AVERAGE  MIXTURES  IN  DIFFERENT 

CITIES    WITH    200-MESH    MATERIAL    REMOVED— 1898    AND 

1899. 


Passing  Mesh. 

Year. 

100 

80 

50 

40 

30 

20 

10 

Philadelphia,  Pa.  . 
Chicago,  111  
Kansas  City,  Mo.  . 
New  York,  N.  Y.. 
Omaha,  Neb.  . 

22 
21 
17 
17 
17 
16 
16 
15 
11 
10 
10 
7 

18 
17 
19 
17 
16 
14 
12 
13 
14 
7 
6 
7 

30 
44 
37 
30 
34 
38 
30 
35 
25 
23 
50 
23 

14 
10 
10 
13 
15 
15 
19 
17 
14 
26 
26 
26 

7 
4 
8 
10 
8 
7 
10 
10 
12 
13 
4 
13 

5 
3 
5 

8 
6 
6 
8 
6 
13 
11 
2 
11 

4 
1 
4 
5 
4 
4 
5 
4 
11 
10 
2 
10 

1899 
1898 
1898 
1898 
1899 
1899 
1899 

1898 

1899 
1898 

St.  Louis,  Mo  .... 
Boston,  Mass  
Paterson,  N.  J.  .  . 
Trenton,  N.  J.  ... 
Washington,  D.  C. 
Louisville,  Ky.  .  .  . 
Youngstown,  O.  . 

GRADING   OF  SANDS  IN   AVERAGE  MIXTURES  IN   DIFFERENT 
CITIES  WITH  13  PER  CENT  OF  200-MESH  DUST. 


Passing  Mesh. 

Year. 

200 

100 

80 

50 

40 

30 

20 

10 

Philadelphia,  Pa.  .  . 
Chicago  111 

13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 
13 

15 
18 
15 
15 
15 
14 
14 
13 
10 
9 
9 
6 

15 
15 
16 
15 
14 
12 
10 
11 
12 
6 
5 
16 

26 
38 
32 
26 
30 
33 
26 
31 
22 
20 
44 
31 

11 
9 
9 
11 
13 
13 
17 
15 
12 
23 
23 
14 

9 
3 
7 
9 
7 
6 
9 
9 
10 
11 
3 
13 

7 
3 
4 
7 
5 
5 
7 
5 
11 
9 
2 
6 

4 
1 
4 
4 
3 
4 
4 
3 
10 
9 
1 
1 

1898 
1898 
1898 
1898 
1899 
1899 
1899 
1898 
1898 
1899 
1899 
1898 

Kansas  City,  Mo.  . 
New  York,  N.  Y  .  . 
Omaha,  Neb  

St.  Louis,  Mo  
Boston  Mass 

Paterson,  N.  J.  .  .  . 
Trenton,  N.  J  
Washington,  D.  C.  . 
Louisville,  Ky  
Youngstown,  O.  .  . 

SURFACE   MIXTURES 


363 


WEIGHT  PER  CUBIC  FOOT  AND  VOIDS  IN  NEW  YORK  SAND, 
WITH  NO  200-MESH  SAND  AND  WITH  13  PER  CENT  DUST 
MADE  UP  ON  THE  GRADING  OF  VARIOUS  CITIES,  COM- 
PARED WITH  THE  SAND  FROM  THESE  CITIES  OF  THE 
SAME  GRADING  AND  WITH  THAT  OF  THE  CITIES  MADE 
UP  ON  THE  NEW  YORK  GRADING. 


Specific 
Grav- 
ity. 

With  no  200. 

With  13  Per  Cent 
Dust. 

Weight 
per  Cubic 
Foot. 

Voids. 

Weight 
per  Cubic 
Foot. 

Voids. 

New  York                         .  .    . 

2.67 
2.63 

2.61 
2.63 
2.63 
2.63 
2.66 
2.68 
2.67 
2.66 
2.62 

109.6 

113.3 
114.1 
110.0 

111.1 

109.0 
113.7 

110.4 
111.8 
110.3 

111.9 
113.8 
109.7 

110.6 
110.0 
110.6 

109.6 
111.8 
106.8 

109.1 
112.5 
107.8 

107.8 
109.6 
110.3 

106.1 
107.2 
112.4 

104.5 
107.2 
108.6 

34.1 

30.9 
30.3 
33.3 

31.6 
32.6 
31.7 

32.6 
31.8 
33.7 

31.7 
31.9 
34.1 

32.6 
32.9 
33.5 

33.9 
32.4 
35.8 

34.6 
32.6 
35.1 

35.2 
34.1 
33.7 

36.5 
34.3 
32.4 

36.0 
34.3 
34.7 

118.9 

124.5 
126.0 
121.4 

123.5 
118.6 
125.6 

122.4 
124.0 
121.9 

122.2 
124.0 
121.1 

121.0 
122.2 
121.4 

120.5 
124.2 

118.8 

120.4 
123.2 
119.1 

119.4 
121.7 
121.5 

119.0 
117.3 
124.0 

115.7 
117.3 
120.4 

28.5 

24.0 
23.1 
27.2 

24.1 

26.9 
24.5 

25.3 
24.3 
26.7 

25.4 
25.7 
27.1 

26.2 
25.4 
27.1 

27.3 
25.0 
28.6 

27.9 
26.2 
28.1 

28.2 
26.8 
27.0 

26  8 
26.2 
25.5 

29.1 
28.2 
27.6 

Omaha,  N.  Y.      "      

N.  Y.,  Omaha      "      

Trenton,  local  grading    

Trenton,  NY       "      

N.  Y.,  Trenton      '  '      

Kansas  City,  local  grading.  .  .  . 
Kansas  Citv,  N.  Y.      "      
N.  Y.,  Kansas  City     "      

St.  Louis,  local  grading  

St   Louis  NY      " 

N  Y  ,  St  Louis      '  ' 

Paterson  ,  local  grading  

Paterson,  N.  Y.      "       

N  Y  ,  Paterson      '  ' 

Buffalo,  local  grading  

Buffalo,  NY       "      

N.  Y.,  Buffalo      "      

Chicago,  local  grading 

Chicago,  NY       "      

N.  Y.  ,  Chicago      '  '      

Philadelphia  local  grading.  . 
Philadelphia,  N.  Y.      " 
N.  Y.,  Philadelphia      "      .... 

Washington,  local  grading.  .  .  . 
Washington,  N.  Y.      "       
N.  Y.,  Washington     "       

Louisville,  local  grading 

Louisville,  N.  Y       " 

N.  Y.,  Louisville      "      .... 

364 


THE  MODERN  ASPHALT  PAVEMENT. 


In  the  preceding  determinations  of  voids  in  different  local 
sands  the  sands  have  been  freed  from  all  200-mesh  grains  before 
adding  the  filler.  In  practice  these  sands  always  contain  from 
1  per  cent  of  this  material  in  Chicago  to  13  per  cent  in  Buffalo. 
Where  so  much  200-mesh  material  not  dust  is  present  the  full 
amount  of  filler  cannot  always  be  used.  The  actual  average 
amount  of  200-mesh  sand  in  the  supplies  of  the  special  cities , 
which  have  been  examined,  and  that  of  the  filler  used  in  1899, 
with  the  percentage  of  the  latter  passing  a  200-mesh  sieve,  is 
given  in  the  following  table : 

AVERAGE  PER  CENT  OF  SAND  PASSING  200-MESH  TAKEN 
FROM  WEEKLY  REPORTS;  ALSO  PER  CENT  USED  IN 
MIXTURE. 


City. 

Year. 

Average 
Per  Cent 
Passing 
200-Mesh. 

Average 
Per  Cent 
Dust  in 
Mixture. 

Per  Cent 
Dust 
Passing 
200-Mesh. 

Per  Cent 
200  Dust 
Added. 

Total 
200  Sand 
and  Dust. 

12.6 
9.5 

10.5 
15.6 
13.0 

8.8 

9.6 
8.7 
16.2 

16.0 

New  York  
Chicago        

1898 
1898 
1899 
1899 
1898 
1899 
1898 
1899 
1898 
1899 
1899 
1899 

5.0 
1.0 
7.0 
10.0 
6.0 
4.0 
2.0 
6.0 
1.0 
11.0 
8.0 
13.0 

8.0 
10.0 
5.0 
8.0 
10.0 
8.0 
7.0 
6.0 
11.0 
8.0 
7.0 
5.0 

95.0 
85.0 
70.0 
70.0 
70.0 
60.0 

60.0 
70.0 
65.0 

60.0 

7.6 
8.5 
3.5 
5.6 
7.0 
4.8 

3.6 

7.7 
5.2 

3.0 

St  Louis     

Louisville  

Kansas  City  

Omaha  

Trenton 

Paterson 

Youngstown 

Washington  
Boston               .  . 

Buffalo         

In  Buffalo,  with  13  per  cent  of  200  sand,  only  3  per  cent  of 
filler  can  be  used,  while  in  Chicago,  with  only  1  per  cent,  8.5  per 
cent  or  more  is  used.  The  total  per  cent  of  200-mesh  sand  and 
dust  in  many  cases  is  below  the  amount  which  should  be  found 
in  a  good  mineral  aggregate,  but  it  must  be  remembered  that 
nearly  3  per  cent  of  200-mesh  filler  is  contributed  to  the  mixture 
by  the  fine  mineral  matter  where  a  Trinidad  asphalt  cement  is 
in  use.  Where  Bermudez  asphalt  is  the  cementing  material  an 
additional  amount  of  filler  is  of  course  required. 


SURFACE   MIXTURES. 


365 


If  all  these  sands  are  taken  and  enough  dust  added  to  make 
the  total  200-mesh  material  in  the  aggregate  up  to  15  per  cent 
the  voids  in  these  aggregates  can  be  determined  and  the  influence 
of  the  presence  of  the  200-mesh  sand  investigated.  This  has 
been  done  and  the  results  follow: 


WEIGHT  PER  CUBIC  FOOT  AND  VOIDS  IN  THE  AVERAGE 
SAND  OF  1899  FROM  VARIOUS  CITIES,  WITH  THE  AVERAGE 
AMOUNT  OF  200-MESH  SAND  AND  ENOUGH  FILLER  ADDED 
TO  BRING  IT  UP  TO  15  PER  CENT,  PASSING  200-MESH,  AND 
WITH  200-MESH  SAND  REMOVED  AND  REPLACED  BY  FILLER. 


City. 

Average 
200  Sand. 

Amount 
Dust 
Added. 

Weight  per  Cu  Ft. 

Voids. 

Without 
200-Mesh 
Sand. 

With 
200-Mesh 
Sand. 

Without 
200-Mesh 
Sand. 

With 
200-Mesh 
Sand. 

New  York 

5.0 
1.0 

7.0 
10.0* 
6.0 
4.0 
2.0 
6.0 
11.  Of 
13.0 
4.0 

10.0 
14.0 
8.0 
5.0 
9.0 
11.0 
13.0 
9.0 
4.0 
2.0 
11.0 

118.9 
120.4 
122.2 
115.7 
122.4 
124.5 
123.5 
121.0 
119.0 
120.5 
119.5 

120.4 
120.7 
121.1 
114.5 
121.4 
125.3 
125.2 
121.2 
117.4 
117.0 
120.9 

28.5 

27.9 
25.4 
29.1 
25.3 
24.0 
24.1 
26.2 
28.8 
27.3 
28.2 

27.6 
27.7 
25.8 
30.0 
26.0 
23.6 
23.0 
26.0 
28.4 
29.4 
27.3 

Chicago      .  .  .*  

St   Louis    

Louisville    

Kansas  City  

Omaha  
Trenton  
Paterson        

Washington    .... 

Buffalo           

Philadelphia  

*  Largely  fine  loam  acting  as  a  filler. 

t  Largely  crushed-stone  dust  acting  as  a  filler. 


With  only  1  per  cent  of  200  sand,  as  in  Chicago,  little  difference 
is  occasioned,  but  in  Buffalo,  with  13  per  cent  of  200  sand,  the  voids 
are  greater  with  the  sand  than  with  this  taken  out  and  substi- 
tuted by  filler.  Where  the  200-mesh  material  in  the  sand  is  more 
of  the  nature  of  filler  than  sand  there  is  little  difference,  but  if 
the  200-mesh  material  is  really  sand  of  the  largest  size  which  will 
pass  a  200  sieve  the  difference  is  striking.  The  substitution  of 
such  a  sand  for  filler  has  been  made  with  the  sands  from  the  several 
cities  and  the  results  show  the  effect  when  compared  with  those 
obtained  with  filler  on  a  previous  page : 


366  THE  MODERN  ASPHALT  PAVEMENT 

EFFECT  OF  SUBSTITUTION  OF  SAND  FOR  FILLER. 


13  Per  Cent  200-Mesh  Sand. 


Weight  per 
Cubic  Foot. 


Voids. 


New  York 115.6 

Omaha,  local  grading 118 . 6 

Omaha,  N.  Y.      "      118.9 

N.Y.,  Omaha      "      118.0 

Trenton,  local  grading 117.1 

Trenton,  N.  Y.      "      114.6 

N.  Y.,  Trenton     "       120.0 

Kansas  City,  local  grading 115.0 

Kansas  City,  N.  Y.      "      116.8 

N.  Y.,  Kansas  City     "      117.0 

St.  Louis,  local  grading 116.1 

St.  Louis,  N.  Y.      "      117.1 

N.  Y.,  St.  Louis      "      118.2 

Paterson,  local  grading 115.6 

Paterson,  N.  Y.      "      116.9 

N.  Y.,  Paterson      "      118.2 

Buffalo,  local  grading 115.9 

Buffalo,  N.  Y.      "      118.4 

N.Y.,  Buffalo      "      114.8 

Chicago,  local  grading 113  0 

Chicago,  N.  Y.      "      117.6 

N.  Y.,  Chicago      "      115.1 

Philadelphia,  local  grading 113 . 3 

Philadelphia,  N.  Y.      "      112.7 

N.  Y.,  Philadelphia      "      117.0 

Washington,  local  grading 114.8 

Washington,  N.  Y.      "      112.3 

N.  Y.,  Washington  120.2 

Louisville,  local  grading 110 . 9 

Louisville,  N.  Y.      "      112.8 

N.  Y.,  Louisville      "      117.3 


30.5 

27.6 
27.4 
29.1 

28.2 
29.5 

27.8 

29.9 

28.8 
29.7 

29.1 
29.9 
28.9 

29.6 
28.6 
29.0 

30.1 
28.4 
31.0 

32.3 
29.6 
30.8 

33.1 
32.3 
29.7 

31.4 
32.8 

27.8 

32.1 
30.9 
29.5 


200-mesh  sand  is  generally  undesirable  because  it  tends  to 
make  the  mixture  less  stable  and  liable  to  move,  as  has  already 
been  shown  Our  ideal  mixture  should,  therefore,  as  a  rule  con- 


SURFACE   MIXTURES.  367 

tain  none  of  this  material,  and  in  this  respect  the  New  York  mix- 
ture is  at  times  capable  of  some  improvement,  although  at  others, 
with  quite  large  amounts,  an  extremely  satisfactory  result  is 
obtained. 

It  is  evident  from  the  preceding  facts  that  something  besides 
the  mere  grading  of  the  sand  has  large  influence  on  the  character 
of  the  mineral  aggregate  and  the  asphalt  surface  mixture  pre- 
pared from  it,  and  this  can  probably  be  explained  by  consider- 
ation of  the  fact  that  the  shape  of  the  sand  grains  which  are  of 
size  to  pass  any  given  sieve  may  be  so  entirely  different  that  they 
fit  together  with  different  degrees  of  compactness,  while  the  power 
of  adsorption  l  of  the  surface  of  the  sand  grams  will  have  an  equal 
influence.  This  is  not  astonishing  from  what  has  been  observed 
in  regard  to  the  character  of  various  sand  supplies  when  the 
subject  of  sand  was  under  consideration. 

Further  Characteristics  Indicative  of  the  Properties  of  Old 
and  New  Asphalt  Surfaces. — In  addition  to  the  consideration  of 
the  preceding  characteristics  in  judging  a  surface  mixture,  cer- 
tain of  its  physical  properties  or  those  of  old  surfaces,  if  one  of 
these  is  under  examination,  must  be  determined,  such  as  its  density 
and  capacity  for  absorbing  moisture,  while  others  may  throw 
some  light  on  the  nature  of  old  surfaces,  more  especially  such  as 
their  tensile,  crushing,  and  shearing  strength.  Old  surfaces  can 
also  be  reheated  and  the  general  appearance  of  the  mixture  in 
this  condition  noted,  including  the  surface  of  a  pat  and  the  stain 
on  a  pat  paper2  made,  at  carefully  regulated  temperatures,  as 
with  a  new  mixture. 

Density. — The  density  of  the  best  mixtures  when  thoroughly 
compacted  either  by  traffic  or  in  the  laboratory,  as  illustrated 
by  that  turned  out  in  New  York  at  the  present  time,  should  be 
about  2.22  to  2.25  when  made  with  ordinary  limestone  and  2.27 
when  made  with  Portland  cement.  The  density  of  such  a  mix- 
ture calculated  from  that  of  their  constituents  is  about  2.27  and 
2.29,  so  that  hi  this  mixture  but  a  small  volume  of  voids  is  found. 
A  comparison  with  these  figures  of  the  actual  density  of  old 
street  surfaces  which  have  been  examined  is  therefore  of  value. 
1  See  page  360.  2  See  pages  353  to  356. 


368 


THE  MODERN  ASPHALT  PAVEMENT. 


In  the  old  surfaces  as  they  exist  in  the  streets  of  many  cities 
of  the  country  densities  of  from  1.89  to  2.26  were  found.  That 
on  Dodge  Street  in  Omaha  had  the  latter  density,  and  two  good 
surfaces,  one  from  Warwick  Boulevard  in  Kansas  City,  laid  in 

1892,  and  one  from  Cumming  Street  in  Omaha,  laid    in    1893, 
had  a  density  of  2.24.     These  densities  are  nearly  theoretical,  and 
such  surfaces  should  be  able  to  keep  out  the  water.     Howard 
Street  in  Omaha,  laid  in  1895,  has  a  density  of  only  1.89,  and  Ohio 
Street  in  Chicago,  laid  in  1894  by  the  Standard  Company,  has  a 
density  of  2.04.     Both  of  these  pavements  are  cracked,  the  former 
very  badly.     Attempts  to  compress    the    latter    mixture  in  the 
laboratory  resulted  in  obtaining  a  no  greater  density. 

It  is  not  always  the  case,  however,  that  a  surface  of  high  density 
does  not  crack  or  the  reverse.  In  Omaha,  Dodge  Street,  laid  in 

1893,  has  a  density  of  2.26,  but  it  has  cracked  probably  because 
the  bitumen  was  too  hard.     In  Chicago,  Tripp  Avenue,  with  a 
density  of  2.21,  has  cracked,  as  has  Walrond  Avenue  in  Kansas 
City,  with  2.24,  for  the  same  reason.     Baltimore  Avenue  in  Kansas 
City,  of  a  density  of  only  2.11,  has  not  cracked,  nor  has  Thirty-ninth 
Street  in  Omaha,  with  a  density  of  2.10.     The  extreme  densities 
of  the  surfaces  examined  in  Chicago,  Omaha,  and  Kansas  City 
were: 


Chicago. 

Omaha. 

Kansas  City. 

Good  surfaces: 
High  density  
Low        " 

2.20 
2  16 

2.24 
2  10 

2.24 
2  11 

Medium  surfaces 
High  density.   .  .  . 
Low        "      .... 
Cracked  surfaces 
High  density.    .  .  . 

LOW     "!!.!! 

2.15 
2.04 

2.26 
2.09 

2.21 
1.89 

2.15 
2.13 

It  seemed  possible  that  a  low  density  might  be  due  to  lack  of 
compression  in  surfaces  laid  in  winter.  The  average  density  of 
the  summer  surfaces  as  compared  with  those  laid  after  Novem- 
ber first  in  Kansas  City  and  Chicago  seems  to  confirm  this  idea, 


SURFACE   MIXTURES. 


369 


but  in  Omaha  the  density  is  slightly  in  favor  of  the  one  winter 
surface  examined. 


Summer 
Pavements, 
Density. 

Winter 
Pavements, 
Density. 

Cracked 
Good 

Cracked 
Good 

Badly  ci 
Medium 
Good 

KANSAS 
pavements  

CITY,  Mo. 

2.235(1)  l 
2.201  (3) 

jo,  ILL. 

2.155(5) 
2.183(2) 

L,  NEB. 

2.180(2) 
2.170(9) 

2.145(3) 
2.136(2) 

2.080(1) 

2.182(1) 
2.184(2) 

CHICAC 
pavements 

n 

OMAHJ 

"acked  pavements, 
good 

1  Number  of  surfaces  examined. 

It  must  be  remembered,  however,  that  variations  in  the  rela- 
tions of  bitumen  to  sand  may  make  a  marked  difference  in  the 
densities,  since  the  greater  the  percentage  of  bitumen  in  a  mixture 
the  lower  will  be  its  volume  weight;  that  is  to  say,  an  excess  of 
bitumen  added  to  an  aggregate  will  lower  the  density  as  much 
as  a  deficiency.  The  density  of  the  densest  mineral  aggregate 
before  the  addition  of  bitumen  has  been  found  to  be  2.00  in  Omaha, 
the  lowest  1.86  in  Louisville.  It  would  not  be  expected,  there- 
fore, that  a  mixture  having  low  voids  would  have  the  same  gravity 
in  Louisville  as  in  Omaha. 

Capacity  for  Absorbing  Water. — Surfaces  will  absorb  water 
in  amount  varying  with  the  density  and  the  percentage  of  bitu- 
men which  they  contain.  With  the  New  York  mixture  the  amount 
of  water  absorbed  by  it  in  milligrams  per  square  inch  and  in  pounds 
per  square  yard  when  a  thoroughly  compacted  cylinder  of  the 
above  density  is  immersed  in  it  for  various  lengths  of  time  is  as 
follows.  See  table  on  page  370. 

It  appears  that  more  water  is  absorbed  in  the  first  day's  immer- 
sion than  in  any  subsequent  day  and  that  it  diminishes  in  a  good 
mixture  as  time  goes  on.  When  the  New  York  mixture  is  made 
with  bitumens  of  different  origin  the  amount  of  water  absorbed 


370 


THE    MODERN    ASPHALT    PAVEMENT 


WATER  ABSORBED  BY  CYLINDER  OF  NEW  YORK  TRINIDAD 
LAKE  ASPHALT  MIXTURE,  DENSITY  2.24,  WHEN  IM- 
MERSED FOR  DIFFERENT  PERIODS. 


Time. 

Milligrams  per 
Square  Inch. 

Total. 

Pounds  per 
Square  Yard. 

Total. 

1   day.  . 

.0169 

.0480 

2  days  

.0021 

.0190 

.0060 

0540 

7     "    

.0092 

.0282 

.0263 

.0803 

15     "    . 

0045 

0327 

0127 

0930 

28     '  '    .  . 

0035 

0362 

0101 

1031 

will  vary.  This  is  illustrated  by  some  data,1  wherein  it  is  seen 
that  Trinidad  asphalt-surface  mixtures  are  quite  as  impervious 
as  those  made  with  other  asphalts  and  after  a  lengthy  exposure 
in  running  water  are  able  to  resist  impact  better  than  any  others. 

Comparison  of  Street  Surfaces  with  New  York  Mixture. — A 
comparison  of  the  absorption  of  water  by  some  of  the  typical 
surfaces  from  old  streets  in  the  western  cities  with  that  absorbed 
by  the  New  York  mixture  will  be  of  interest.  See  results  tabulated 
on  pages  371  and  372. 

These  results  show  that  the  absorption  in  the  old-time,  poorly 
graded  surfaces  is  in  inverse  proportion  to  the  amount  of  bitumen 
they  contain  and  that  those  of  high  density,  unless  they  contain 
enough  bitumen  to  fill  the  voids,  as  shown  by  a  paper  test,  gain 
more  than  less  dense  mixtures  with  sufficient  bitumen, 

Such  a  surface  as  that  on  Thirty-ninth  Street,  Omaha,  which 
the  pat  paper  shows  is  excessively  rich  in  asphalt  cement,  excludes 
water  better  than  the  New  York  mixture,  as  does  the  rich  War- 
wick Boulevard  surface  from  Kansas  City.  The  old  Howard 
Street  surface  with  less  than  8  per  cent  of  bitumen,  of  course, 
absorbs  more  water  than  any  of  the  others  which  were  examined. 
The  peculiarities  of  the  other  surfaces  appear  from  an  inspection 
of  the  results  in  the  table.  Twenty-sixth  Street  in  Omaha,  although 
it  has  cracked  some,*  absorbs  a  comparatively  small  amount  of 
water,  but  it  must  be  remembered  that  water  absorption  results 
more  in  disintegration,  scaling,  and  rotting  than  in  cracking. 

1  See  page  468. 


SURFACE  MIXTURES. 


371 


WATER  ABSORBED  BY  CYLINDERS  OF  OLD  SURFACE. 


Twt  No. 


Street. 


Density  of 

Compacted 

Cylinder. 


Stain  on  Pat  Paper. 


NEW  YORK  MIXTURE. 


Fifth  Ave.  mixture 2.24  Heavy 

KANSAS  CITY,  Mo. 

21440        Baltimore  Ave.— good 2.240  Heavy 

21442         Garfield  Ave.— cracked 2 . 158  Very  light 

21445  Walrond  Ave.— cracked 2. 195  Heavy 

21446  Warwick  Blvd.— good 2 . 274        Very  heavy,  coarse 

21447  Seventh— good 2.248  Medium 

OMAHA,  NEB. 

21448  23d— cracked 2. 142  Strong 

21456         20th— medium  good 2 . 205  Medium 

21461         39th— good 2.209  Very  heavy 

23253  Gumming — good 2 . 235  Medium 

23254  26th— cracked 2.217 

23256  Capitol — medium  good 2 . 210  Heavy 

23257  Howard— cracked 1 .904  None 

CHICAGO,  ILL. 

21431         Prairie— good 2.231  Heavy 

21433        Tripp— cracked 2 . 193  Strong 

21435         So.  Park  Ave.— cracked 2.156  Strong 

21438        Washington  Blvd— good 2.201  Medium 


Why  the  Standard  Mixture  is  Satisfactory. — The  standard 
mixture  which  has  been  suggested  by  the  author  and  which  is 
now  universally  laid  under  his  supervision  where  this  is  possible, 
on  streets  of  heavy  traffic  and  elsewhere,  has  been  arrived  at  by 
the  examination  of  surfaces  which  have  proved  successful  and 
not  by  any  theoretical  reasoning  or  experimenting.  Practice 
during  the  last  eleven  years  has  shown  that  such  a  mixture  is 
successful.  The  results  of  laboratory  investigations  on  the  sub- 
ject have,  however,  made  it  possible  to  explain  theoretically  and 
with  a  good  deal  of  satisfaction  why  the  standard  mixture  has 
been  a  satisfactory  one.  The  greatest  factors  in  the  construction 


372 


THE    MODERN    ASPHALT    PAVEMENT 


WATER  ABSORBED   BY  CYLINDERS  OF  OLD  SURFACE. 

ABSORPTION,  POUNDS  PER  SQUARE  YARD. 


Test  No. 

IDay. 

2  Days. 

7  Days. 

15  Days. 

28  Days. 

Add. 

Total. 

Add.    i  Total. 

Add.       Total. 

Add. 

Total 

NEW  YORK  MIXTURES. 
.0480J   .0060|   .0540J   .0263|    .0803|   .0127|   .0930|   . 

KANSAS  CITY,  Mo. 


.1031 


21440 

.089 

.029 

.125 

.113 

.238 

.096 

.334 

.146 

.480 

21442 

.141 

.063 

.204 

.342 

.546 

.354 

.900 

.379 

1.279 

21445 

.095 

.080 

.175 

.231 

.406 

.357 

.763 

.580 

1.343 

21446 

.050 

.017 

.067 

.068 

.134 

.074 

.208 

.119 

.327 

21447 

.115 

.065 

.181 

.319 

.499 

.286 

.785 

.434 

1.219 

OMAHA,  NEB. 

21448 

.128 

.051 

.178 

.292 

.469 

.426 

.896 

.693 

1.589 

21456 

.106 

.060 

.166 

.234 

.399 

.185 

.585 

.267 

.852 

21461 

.032 

.012 

.045 

.052 

.097 

.046 

.142 

.091 

.234 

23253 

.062 

.027 

.089 

.125 

.215 

.146 

.361 

.210 

.571 

23254 

.068 

.025 

.093 

.118 

.211 

.133 

.344 

.226 

.570 

23256 

.066 

.043 

.109 

.415 

.524 

23257 

.273 

.103 

.376 

.531 

.907 

.767 

1.674 

.505 

2.259 

CHICAGO,  ILL. 

21431 

.058 

.017 

.075 

.069 

.144 

.073 

.217 

.103 

.319 

21433 

.096 

.043 

.139 

.221 

.360 

.282 

.642 

.386 

1.028 

21435 

.106 

.053 

.159 

.291 

.450 

.338 

.787 

.473 

1.253 

21438 

.089 

.037 

.126 

.208 

.334 

.241 

.575 

.309 

.884 

of  a  successful  asphalt  surface  is  that  the  mixture  shall  be  so 
dense  as  to  resist  the  action  of  water  and  impact  and  at  the  same 
time  contain  sufficient  bitumen  to  permit  its  responding,  without 
cracking,  to  a  sudden  fall  in  temperature.  The  standard  mixture 
seems  to  offer  these  advantages  in  a  way  not  supplied  by  a  coarser 
and  more  carelessly  prepared  mixture. 

The  only  way  to  keep  water  out  of  an  asphalt  surface  is  to 
have  the  voids  in  the  surface  mixture  as  small  as  possible  in  size, 
but  not  necessarily  so  in  volume,  to  fill  them  with  bitumen  of  a 
consistency  which  will  permit  of  contraction  and  to  stiffen  the 
latter  with  a  proper  amount  of  filler  which  will  alone  permit  of 
the  use  of  a  sufficiently  soft  cement.  If  the  interstitial  spaces 
are  few  in  number  but  large  in  size,  the  asphalt  occupying  them 
will  be  in  such  large  masses,  if  the  voids  are  entirely  filled,  that 


.SURFACE    MIXTURES.  373 

they  will  easily  yield  to  stress  and  cause  the  surface  to  mark  and 
push  and  the  pavement  to  appear  soft.  If  the  voids  are  not  filled 
water  quickly  enters  and  destroys  the  pavement.  If  fine  sand 
is  introduced  in  proper  proportions  the  size  of  the  interstitial 
spaces  is  much  reduced,  the  volume  of  the  masses  of  asphalt  filling 
them  is  reduced  in  the  same  way,  and  the  voids  can  be  thoroughly 
filled  without  danger  of  movement.  This  is  made  more  certain 
by  the  introduction  of  a  filler  into  the  cement,  thus  stiffening  it  as 
it  exists  between  the  voids.  The  function  of  a  filler  can  be  seen 
by  rolling  out  two  cylinders  of  a  cement  of  the  same  consistency, 
one  containing  25  per  cent  of  filler  and  the  other  none.  Their 
ductility  or  elongation  under  stress  is  then  found  to  be  as  follows: 

AT  78°  F. 

Without  filler— elongation 20 . 6% 

With  25  per  cent  filler — elongation 34 . 5 

The  part  played  by  the  filler  in  an  asphalt  surface  mixture 
is  thus  made  apparent. 

Fine  sand  of  100-  and  80-mesh  size  is  desirable,  since  it  is  evi- 
dent that  grains  of  this  size  if  introduced  in  the  proper  propor- 
tions among  coarser  sand  grains  must  reduce  the  size  of  the  inter- 
stitial spaces  between  the  grains  even  if  they  do  not  reduce  the 
volume  of  the  latter.  In  this  way  they  play  an  important  part 
in  the  stability  of  the  pavement,  but  they  play  a  still  more  important 
part  in  making  it  possible  to  use  a  desirable  amount  of  filler  in 
the  mixture.  In  the  early  days  of  the  industry,  as  it  was  carried 
on  in  the  city  of  Washington,  it  was  possible  to  use  only  a  very 
small  amount  of  filler  in  the  surface  mixture  and  this  never 
exceeded  3  or  4  per  cent.  If  a  larger  amount  was  added,  either 
there  or  elsewhere,  where  coarse  sands  were  employed,  it  was 
found  that  when  an  attempt  was  made  to  lay  the  mixture  upon 
the  street  it  would  not  rake  or  spread  with  ease  and  was  in  a  con- 
dition which  was  known  as  "  bally."  It  was  impossible,  there- 
fore, under  such  conditions  to  attempt  to  close  up  the  surface 
of  the  finished  pavement  by  the  use  of  large  percentages  of  filler, 
although  attempts  were  made  to  do  so.  When  it  was  found  that 
the  most  desirable  surfaces  contained  a  considerable  percentage 
of  filler  not  intentionally  introduced  into  them,  and  that  this 


374  THE    MODERN   ASPHALT   PAVEMENT 

was  accompanied  by  a  similar  amount  of  100-  and  80-mesh 
sand  grains,  attempts  to  duplicate  these  mixtures  with  the  fine 
sand  present  showed  that  in  the  presence  of  the  latter  much  higher 
percentages  of  filler  could  be  added  without  resulting  in  a  "  bally  " 
condition  of  the  hot  mixture  on  the  street.  A  consideration  of  this 
state  of  affairs  will  quickly  show  that  this  is  due  to  the  fact  that 
in  the  coarse  sand  where  the  size  of  the  spaces  between  the  indi- 
vidual grains  were  large  there  was  an  opportunity  for  the  filler  to 
become  balled  up  with  the  comparatively  large  masses  of  asphalt 
cement  present  there,  but  when  the  fine  sand  was  introduced  this 
material  as  it  was  tossed  around  in  the  mixer  in  a  hot  condition  it 
broke  up  these  balls  and  made  a  smooth  and  homogeneous  mix- 
ture which  could  be  raked  out  on  the  street  with  ease.  The  value 
of  sand  of  100-  and  80-mesh  sizes  is,  therefore,  to  be  attributed 
to  the  two  causes  mentioned  above:  one,  its  reduction  of  the  size 
of  the  spaces  between  the  individual  sand  grains,  and,  secondly, 
to  the  fact  that  it  permits  the  use  of  a  proper  amount  of  filler 
in  the  mixture  by  preventing  the  collection  of  the  filler  into  bally 
masses. 

SUMMARY. 

The  preceding  chapter  consists  of  an  elaborate  discussion  of 
the  theory  of  asphalt-surface  mixtures  which  does  not  admit  of 
summarization  beyond  the  statement  that  the  construction  of  a 
standard  mixture  is  dependent  upon  an  intimate  knowledge  of 
the  behavior  of  sand  and  the  complete  mineral  aggregate  towards 
the  bitumen  and  of  the  finished  surface  mixture  towards  its 
environment. 

It  shows  that  an  asphalt  surface  to  be  successful  must  be  so 
constructed  as  to  resist  weathering  and  impact,  which  are  the  two 
most  serious  enemies  of  such  a  surface,  and  it  also  shows  how 
this  can  be  done. 

As  the  surface  mixture  is  one  of  the  most  important  elements 
of  the  pavement  the  data  collected  here  will  be  of  great  interest 
to  the  asphalt  expert  or  the  person  desiring  to  make  himself  one, 
and  also  to  a  very  considerable  extent  to  the  general  reader  in 
revealing  the  amount  of  skill  which  is  necessary  in  handling  the 
material  which  enters  into  the  composition  of  an  asphalt  surface. 


CHAPTER  XVII. 
ASPHALTIC  OR  BITUMINOUS  CONCRETE. 

The  term  asphaltic  or  bituminous  concrete  has  been  in  use 
for  many  years  to  denote  a  concrete  in  which  asphalt  or  some  other 
bituminous  substance  has  been  used  as  a  cementing  material 
for  a  mineral  aggregate  instead  of  hydraulic  cement.  Such  a 
concrete  has  been  employed  particularly  as  a  foundation  for 
heavy  machinery,  the  vibration  of  which  it  has  been  desired  to 
do  away  with  where  this  is  a  nuisance.  Owing  to  its  elasticity 
and  lack  of  rigidity,  it  absorbs  and  does  not  transmit  shock.1 

As  a  pavement  or  roadway  bituminous  concrete  in  which  coal 
tar  was  the  cementing  material  was  exploited  to  a  very  large  extent 
nearly  half  a  century  ago  in  the  United  States.  Roadways  of 
this  description  were  laid  in  Washington,  D.  C.  in  the  early  J70's, 
among  them  one  on  Connecticut  Avenue  by  C.  E.  Evans  in  1873, 
under  a  contract  dated  August  7,  1872.  This  pavement  was  a 
failure  owing  to  the  character  of  the  cementing  material  and  was 
resurfaced  and  covered  up  with  a  new  one  after  a  short  time.  It 
remained  in  place,  however,  as  a  foundation  of  the  roadway, 
until  1906,  when  it  was  removed,  on  repaving  the  street,  and  the 
construction  of  a  hydraulic  concrete  foundation.  The  author 
was  present  when  the  old  surface  was  torn  up,  and  collected 
specimens  of  the  original  Evans  concrete  as  being  of  interest  and 

1  See  Delano,  "Twenty  Years'  Practical  Experience  of  Natural  Asphalt 
and  Natural  Bitumen,"  London,  E.  &  F.  N.  Spon,  1893.  Malo,  "L'As- 
phalte.  Son  Origine,  Sa  Preparation,  Ses  Applications,"  Paris,  1866  and 
1898.  Letouze  et  Loyeau,  "Traite  pratique  des  Travaux  en  Asphalte/' 
E.  Bernhard  et  Cie,  Paris,  1897. 

375 


376 


THE  MODERN   ASPHALT  PAVEMENT. 


ASPHALTIC    OR    BITUMINOUS    CONCRETE. 


377 


as  illustrating  the  earliest  bituminous  concrete  in  use  as  a  road- 
way, which  has  been  preserved.     A  sawn  section  of  this  pavement 


is  shown  in  Fig.  10.  It  will  be  seen  that  the  mineral  aggre- 
gate in  this  bituminous  concrete  consists  of  broken  stone  of 
various  sizes,  sand  and  coal  tar  as  a  cementing  material.  This 


378  THE  MODERN  ASPHALT  PAVEMENT. 

is  more  strikingly  shown  by  an  analysis  of  the  material  which 
resulted  as  follows. 

EVANS'   CONCRETE   PAVEMENT,    1873. 

Entire  Mineral 

Pavement.  Aggregate. 

Bituminous  matter  soluble  in  CS2 3 . 0% 

Mineral  matter  passing  200-mesh  screen 3.2  3.4%  3.4 

10     "         "     37.1     37.1  38.2     38.2 

"           «           "          8     "         "     2.7  2.8 

«           "           "            i  inch     "     10.5     13.2  10.8     13.6 

"           "           "            %    "        "     14.3  14.7 

"           "           "             f    "        "     14.7  15.2 

"           "           "           1      "        "               .    14.5     43.5  14.9     44.8 


100.0  100.0 

Density  of  concrete 2 . 73 

"        "  stone 2.86 

"  sand 2.65 

Voids  in  mineral  aggregate 23 .7% 

The  concrete  does  not  differ  in  a  great  degree  from  similar 
material  which  has  been  used  as  street  roadways  within  the  last 
few  years,  at  least  as  far  as  the  grading  of  the  mineral  aggregate 
is  concerned,  as  will  appear  from  analyses  which  follow.  Much 
of  it  was  laid  in  Washington  at  the  time  mentioned,  but  all  of 
it  was  unsatisfactory  and  required  resurfacing  within  a  few  years. 
It  is  of  interest  only  as  showing  that  a  bituminous  concrete  was 
recognized  as  long  ago  as  1873  as  a  possible  material  for  paving 
purposes. 

Asphaltic  concrete,  as  far  as  the  author  is  informed,  was  first 
proposed  for  use  as  a  pavement  in  1896.  A  sidewalk  of  this 
material  was  constructed  on  West  Avenue  at  Sixth  Street,  in 
Long  Island  City,  N.  Y.,  at  the  plant  of  the  Barber  Asphalt 
Paving  Company  at  that  point.  The  development  of  the  concrete 
used  was  the  result  of  some  investigations  conducted  to  determine 
whether  a  satisfactory  material  of  this  description  could  be  assem- 
bled from  a  well  graded  mineral  aggregate  and  an  asphaltic  cement 
which  would  be  suitable  for  lining  a  canal.  In  order  to  obtain 


ASPHALTIC  OR    BITUMINOUS    CONCRETE. 
COAL-TAR  CONCRETES,  1902-1906. 


379 


Cleveland, 
Ohio. 

1902 

St.  Louis, 
Mo. 

1903 

St.  Louis, 
Mo. 

1904 

Toronto, 
Ont. 

1904 

Water- 
bury, 
Conn. 

1905 

Soluble  in  CS2  .  . 

3  9% 

3  4% 

5  0% 

5  5% 

4   30? 

Passing  200  screen  

7.1 

2.9 

5.6 

50 

55 

100      "      

18.8 

12.0 

23.8 

26  0 

21  9 

1-inch  screen  .  .  . 
\    "        " 

13.9 

4.2 
6  6 

8.2 
19  0 

14.7 
17  5 

6.3 
3  6 

3        11               (f 

16  8 

10  8 

i  "    ••   ::: 

Retained    1      "        "       ... 

56.3 

55.6 
15.3 

38.4 
.'0 

8.4 
6  1 

23.3 
24  3 

Total 

100  0 

100  0 

100  0 

100  0 

100  0 

S&- 
Mass'. 

1905 

Cam- 
bridge, 
Mass. 

1905 

Boston, 
Mass. 

1905 

Lynn, 
Mass. 

1905 

Port 
Huron, 
Mich. 

1906 

Soluble  in  CS2    . 

5  3% 

5   3% 

4  8% 

6   2%* 

6   Q% 

Passing  200  screen  
"       100      "       

3.3 
29  4 

4.4 
30  9 

4.7 
26  5 

5.5 

19  0 

1.8 

13  7 

'  l            £-inch  screen  .  .  . 

tt              i     <<         (f 

2 
tt                     3       <(               <( 

((                  J          tl               ll 

Retained   1      "         "      '.'.'. 

11.4 
3.3 
12.8 
12.5 
22.0 

15.9 
21  A 
15.6 
6.5 
.0 

14.4 
24.0 
23.0 
2.6 
.0 

10.5 
23.1 
23.1 
10.1 
2.5 

13.2 
10.9 
5.5 
4.6 
43.4 

Total  

100  0 

100  0 

100  0 

100  0 

100  0 

*  Percentages  of  components  used. 

a  mineral  aggregate  with  a  small  percentage  of  voids,  it  was 
recognized  that  it  would  be  necessary  to  combine  the  coarsest 
stone  which  was  to  be  used  with  finer  stone  to  fill  the  voids  in 
the  coarser,  and  this  again  with  sand  and  fine  mineral  matter  to 
further  reduce  them.  The  relative  proportions  were  determined 
by  experiments. 

In  the  actual  production  of  this  concrete  mixture,  crushed 
stone,  the  largest  particles  of  which  would  pass  a  screen  with 
openings  three-quarters  of  an  inch  in  diameter,  but  containing 
a  considerable  amount  of  quarter  inch  material,  was  heated  and 
separated  into  two  sizes,  coarse  particles  and  those  passing  a 


380  THE  MODERN  ASPHALT  PAVEMENT. 

screen  with  openings  three-eighths  inch  in  size.  Sand,  such  as 
was  ordinarily  used  in  the  paving  business,  was  heated  separately. 
Finely  ground  limestone  was  used  cold.  These  four  components 
were  then  mixed  while  the  first  three  were  hot,  and  to  them  was 
added  an  asphalt  cement  of  proper  consistency  in  the  predeter- 
mined proportions.  The  resulting  concrete  mixture  was  tamped 
into  a  wooden  form  from  which  the  resulting  block  was  removed 
on  cooling.  Its  dimensions  were  3X4X1  in  feet.  It  was  a  very 
successful  piece  of  bituminous  concrete,  and  after  exposure  to  the 
sun  and  weather  for  nine  years  had  preserved  its  form  and  showed 
no  signs  of  deterioration.  It  was  very  carefully  analyzed  in 
1905,  with  the  following  results : 

Test  number 81662 

Bitumen 7.9% 

Passing  200-mesh  screen 9.3         9.3 

"          10      "         "      34.7 

"  8      "         "      6 

' '  |-inch  screen 6.1         6.7 

\    "         "      31.6 

"  1      "         "      9.8 

Retained    1      "         "  .0       41.4 


100.0 
Voids  in  mineral  aggregate 15.0% 

This  concrete,  as  appears  from  the  above  data,  consists  of 
a  well  graded  mineral  aggregate,  the  voids  in  which  amount  to 
only  15%  of  its  volume,  cemented  together  into  a  resistant  mass 
by  an  asphalt  cement.  It  was  so  satisfactory  that  its  application 
as  a  surface  for  pavements  at  once  suggested  itself.  In  order  to 
determine  whether  it  could  be  used  in  this  way  practically,  a 
driveway  in  a  store-house  at  the  plant  of  the  Barber  Asphalt 
Paving  Company,  Long  Island  City,  covering  an  area  of  36  square 
yards,  was  laid  with  such  a  concrete,  the  character  of  which  is 
shown  by  the  following  determinations  made  upon  a  sample  of 
the  surface  in  1905,  after  the  roadway  had  been  subjected  to  the 
traffic  of  loaded  vans  for  nine  years,  with  no  repairs. 


ASPHALTIC    OR   BITUMINOUS    CONCRETE  381 

Test  number 80951 

Bitumen 6.2% 

Passing  200-mesh  screen 5.1         5.1 

10     "         rt      33.6 

"           8      "         "      3.1 

"            i-inch  screen 9.3      12.4 

"             \    "         'l      27.0 

1      "        "     15.7 

Retained   1      "         "      0      42.7 

100.0 
Voids  in  mineral  aggregate 14 . 1% 

The  general  similarity  between  the  concrete  of  the  driveway 
and  the  block  is  evident.  The  latter  contains  more  coarse  stone, 
but  the  voids  in  the  mineral  aggregate  are  practically  the  same, 
14.1  as  compared  to  15.0  per  cent  in  the  samples  examined.  The 
fact  that  an  asphaltic  concrete,  the  basis  of  which  is  a  mineral 
aggregate  of  such  compact  and  dense  nature  as  to  contain  a  very 
low  percentage  of  voids,  could  be  turned  out,  in  a  rational  and 
not  an  empiric  way,  on  different  occasions,  and  successfully 
placed  in  forms  and  as  a  roadway  was  thus  demonstrated. 

At  that  time  there  was  no  sidewalk  in  front  of  the  office  and 
laboratory  of  the  Barber  Asphalt  Paving  Company  on  West 
Avenue,  the  building  having  "been  only  recently  completed.  In 
view  of  the  success  met  in  laying  the  driveway,  it  was  decided 
to  construct  this  walk  of  the  same  material,  so  that  its  behavior 

Test  number 82157 

Bitumen 7.3% 

Passing  200-mesh  screen* 8.2         8.2 

"          10      "          "     24.2 

ft  g        ce  it  -j     2 

\ -inch  screen 7.9         9.1 

\    "        "     30.9 

1      "         "     20.3 

Retained   1      "        "     0      51.2 

100.0 
Voids  in  mineral  aggregate 15 . 5% 


382  THE  MODERN  ASPHALT  PAVEMENT. 

might  be  observed  in  the  open  air.  The  area  covered  was  about 
90  square  yards,  and  the  surface  was  supported  upon  a  broken 
stone  and  cinder  foundation.  The  character  of  the  mixture 
laid  is  shown  on  the  bottom  of  preceding  page,  as  determined  in 
1905  from  several  samples  taken  from  the  pavement  at  that  time. 
In  producing  the  preceding  mixture,  the  records  show  that 
the  components  were  combined  in  the  following  proportions : 

Stone,  passing  f-inch  screen 450  Ibs.  =  46 .2% 

"  "       £    "         "      125   "   =  12.8 

Sand,         "       10  mesh  screen 250   "   =  25.6 

Filler,  dust,  60%  passing  200-mesh- 

screen 50   "  =  5.1 

Asphalt  cement 100  "  =  10.3 


975  100.0 

The  mineral  aggregate,  it  will  be  seen,  as  has  already  been 
mentioned,  was  made  up  of  two  sizes  of  stone,  of  sand,  and  a 
filler  in  the  shape  of  a  fine  mineral  dust.  They  were  combined 
in  such  proportions  as  to  make  a  very  dense  aggregate  having 
voids,  varying  on  account  of  some  segregation  in  laying  the  mate- 
rial, of  from  13  to  17  per  cent,  and  averaging  15.5  per  cent.  This 
aggregate  was  assembled  on  the  previously  well  established  prin- 
ciple that  to  accomplish  the  desired  result — a  dense  concrete — 
the  voids  in  the  coarsest  stone  must  be  filled  with  particles  of 
suitably  smaller  size,  and  the  voids  in  this  combination  again 
with  other  still  smaller  ones — in  this  case  sand — and  still  further 
with  material  finer  than  sand — in  this  case  mineral  dust.  The 
actual  proportions  were  worked  out  by  packing  the  materials 
solidly  in  a  box  holding  a  cubic  foot  and  determining  the  percent- 
ages of  each  necessary  to  obtain  the  densest  aggregate. 

The  bituminous  concrete  made  in  this  way  has  given  great 
satisfaction  for  eleven  years.  When  a  demand  arose  for  such  a 
mixture  for  roadways,  as  a  novelty,  it  was  very  evident  that  it 
was  only  necessary  to  duplicate  the  Long  Island  City  mixture 
of  1896.  This  was  done  on  a  considerable  scale  in  Muskegon, 
Mich.,  in  1902,  on  Muskegon  Avenue,  under  the  author's  direction. 
The  area  covered  was  10,736.16  square  yards.  The  mixture  had 


ASPHALTIC    OR    BITUMINOUS    CONCRETE.  383 

the  following  composition,  as  shown  by  a  very  careful  analysis 
made  of  a  specimen  taken  from  the  street  in  1905: 

Test  number 81117 

Bitumen 7.4% 

Passing  200  mesh  screen 7.4         7.4 

10      "        "      34.0 

"           8      "        "      2.8 

"             Hnch      "      11.2       14.0 

"              \    "        "      18.0 

l"     "        "      19.2 

Retained   1      "        "  .0      37.2 


100.0 
Voids  in  mineral  aggregate 16 .8% 

A  comparison  of  these  data  with  those  for  the  mixture  of 
1896  shows  the  striking  resemblance  of  the  two  materials,  al- 
though the  Muskegon  mixture  contained  less  stone.  The  pave- 
ment was,  in  fact,  a  duplication  of  the  Long  Island  City  work.  It 
has  proved  entirely  satisfactory  after  six  years  use. 

In  the  following  year,  1903,  an  asphaltic  concrete  pavement 
was  laid  in  Owosso,  Mich.,  with  a  mixture  having  a  similar  com- 
position, but  containing  more  coarse  stone. 

Test  number 80904 

Bitumen 7.4% 

Passing  200  mesh-screen 5.2         5.2 

"         10      "        "      29.4 

"           8      "        "      2.2 

"             i-inch  screen 3.5        5.7 

"             \    "        "      9.8 

"           1      "        "      33.5 

Retained    1      "        " 9.0      52.3 

100.0 
Voids  in  mineral  aggregate 13 . 2% 

Similar  surfaces  have  been  laid  in  Scranton,  Pa.,  Paterson, 
N.  J.,  Newark,  N.  J.,  in  the  Borough  of  Richmond,  New  York  City, 


384 


THE  MODERN  ASPHALT  PAVEMENT. 


and  elsewhere  in  subsequent  years.     They  have  proved  satis- 
factory on  streets  of  light  traffic  where  street  car  tracks  are  absent, 


FIG.  12.— Asphaltic  Concrete  Sidewalk,  Long  Island  City,  New  York,  1896. 

but,  like  all  pavements,  cannot  be  maintained  against  rails  that 
are  not  rigid.     They  will  not  withstand  heavy  traffic,  as  the 


FIG.  13. — Asphaltic  Concrete  Surface,  Broadway,  Paterson,  N.  J.,  1906. 

coarse  particles  of  stone  ravel  out  under  the  continuous  impact 
of  the  horses'  hoof  and  shoe,  the  commonest  cause  of  deterioration 
of  all  forms  of  street  pavement.  If,  however,  the  asphaltic  con- 


ASPHALTIC    OR   BITUMINOUS  CONCRETE. 


385 


Crete  is  covered  with  an  inch  of  standard  surface  mixture  the 
resulting  pavement  has  been  found  to  exceed  for  durability  any- 
thing that  has  been  hitherto  constructed,  especially  where  there 


is  a  possiblity  of  vibration,  as  along  street  railway  tracks  and  on 
a  base  which  is  not  perfectly  rigid.  There  is  every  evidence 
that  this  form  of  construction  will  be  the  one  to  be  adopted  on 


386 


THE  MODERN  ASPHALT  PAVEMENT. 


streets  of  heavy  traffic  in  the  future,  and  its  use  is  recommended 
by  the  author  where  trying  conditions  are  to  be  met.  This  form 
of  construction  is  shown  in  section  in  Fig.  16. 


Production  of  Asphaltic  Concrete. — Asphaltic  concrete  can  be 
turned  out  in  any  plant  which  is  fitted  for  the  production  of  the 


ASPHALTIC    OR    BITUMINOUS    CONCRETE. 


387 


binder  and  surface  mixture  for  the  ordinary  form  of  sheet  asphalt 
pavement,  with  certain  modifications,  permitting  of  the  separation 
of  the  stone  into  two  sizes  after  it  has  been  heated  in  the  ordinary 
heaters  provided  for  binder  stone  and  storage  in  separate  bins. 
For  this  purpose  the  heated  stone  is  passed  over  a  revolving 


FIG  16. 

apparatus  provided  for  this  purpose.  The  three  materials  are 
then  weighed  or  measured  out  in  the  predetermined  proportions, 
screen  of  sheet  metal  having  perforations  f  inch  in  diameter.  The 
finer  stone  which  passes  the  screen  is  collected  in  one  bin  and 
the  coarser  into  another.  There  is  no  necessity  for  separating  them 
into  a  greater  number  of  sizes.  The  sand  is  heated  in  the  ordinary 


388  THE  MODERN  ASPHALT  PAVEMENT. 

the  dust  or  filler  added,  and  the  combined  aggregate  thoroughly 
mixed  in  the  usual  pug  mill,  after  which  the  asphalt  cement  is 
added  and  the  mixing  continued  until  the  concrete  is  homo- 
geneous. Portions  of  the  mixture  are  then  compacted  under  a  hot 
tamper  upon  a  firm  surface  to  determine  how  satisfactory  it  is. 
The  hot  tamper  should  bring  to  the  surface  of  the  specimen  a 
slight  excess  of  bitumen,  if  this  is  present  in  correct  amount. 
If  the  surface  remains  dry,  more  asphalt  cement  must  be  added, 
but  if  it  is  too  greasy,  it  must  be  reduced.  On  cooling  the  specimen 
may  be  broken. 

If  the  concrete  is  to  be  used  as  a  binder  course,  there  must  be 
no  excess  of  bitumen  and  a  slight  deficiency  of  sand  over  that 
required  to  fill  the  voids  in  the  stone,  as  otherwise  the  surface 
will  be  too  readily  displaced  on  such  a  course  under  traffic. 

The  character  of  the  concrete,  in  either  case,  can  be  determined 
also  by  its  appearance  in  the  truck  after  the  haul  from  the  plant 
to  the  street.  Where  it  is  to  be  used  as  the  surface  to  carry 
traffic,  it  should  have  settled  to  a  compact  mass,  the  top  of  which 
should  show  a  slight  excess  of  bitumen  as  a  rich  coating,  whereas 
if  it  is  intended  for  a  binder  course  no  excess  of  bitumen  should 
appear  and  there  should  be  some  evidence  of  the  coarser  particles 
of  stone  at  the  top  of  the  load. 

In  either  case,  the  asphalt  cement  should  be  much  softer  than 
that  in  use  in  the  ordinary  surface  mixture  containing  sand  alone. 
The  penetration  should  be  about  90,  as  determined  by  the  Bowen 
penetration  machine. 

SUMMARY. 

An  asphaltic  concrete  pavement  is  not  a  novelty.  Such  pave- 
ments have  been  laid  for  over  twelve  years,  and  have  proved 
satisfactory  where  not  exposed  to  heavy  traffic.  On  streets  like 
Broadway,  in  New  York,  it  is  unsatisfactory. 


CHAPTER  XVIII. 
ASPHALT  BLOCKS. 

Pavements  composed  of  blocks  of  asphaltic  concrete  in  which 
the  coarsest  particles  of  the  aggregate  are  no  larger  than  \  or  f 
inch  in  size,  have  been  laid  for  a  great  many  years  with  considerable 
success  on  streets  of  light  or  very  moderate  traffic.  The  idea 
of  making  such  blocks  originated  in  a  crude  way  in  San  Francisco 
in  1869.  The  first  Board  of  Commissioners  of  the  District  of 
Columbia  stated  in  its  report  of  1878  that  an  experimental  piece 
of  pavement  of  this  description  had  been  laid  in  Washington  on 
E  Street,  the  Board  having  been  influenced  to  do  so  by  favorable 
reports  of  its  durability  in  Providence  and  Philadelphia.  It  was 
not,  however,  until  the  application  of  powerful  mechanical  presses 
to  the  compression  of  the  blocks  in  1880  that  they  proved  at  all 
successful.  60,774  square  yards  of  this  form  of  pavement  had 
been  laid  in  Baltimore  up  to  June  30,  1885,  and  45,000  had  been 
laid  in  Washington  on  a  foundation  of  five  inches  of  bank  gravel 
and  a  cushion  of  two  inches  of  sand.  The  Engineer  Commissioner 
of  the  latter  city  reported  that  the  character  of  the  block  had  much 
improved  in  the  two  preceding  years.  The  blocks  were  four  inches 
deep,  five  inches  wide  and  twelve  inches  long.  Many  of  these 
pavements  are  in  existence  to-day  in  satisfactory  condition,  having 
been  subjected  only  to  the  most  moderate  travel  on  residence 
streets,  and  prove  the  adaptability  of  §uch  surfaces  to  similar 
conditions.  The  blocks  were  of  sufficient  depth  to  support  each 
other  laterally.  By  June  30,  1889,  the  area  of  block  pavements 
in  Washington  had  increased  to  117,164  yards,  and  it  had  spread 

389 


390  THE  MODERN  ASPHALT  PAVEMENT. 

to  other  towns,  notably,  Baltimore,  Md.,  and  Chester,  Pa.,  where 
40,000  square  yards  of  block  had  been  laid.  This  form  of  pavement 
made  no  great  further  progress  until  1896,  when  the  amount  reached 
200,000  yards,  33,874  of  this  being  in  the  Borough  of  Man- 
hattan, and  the  blocks  being  4X4X12  inches  in  dimension.  In 
1901  the  block  as  at  present  laid,  3X5X12,  was  brought  out 
and  laid  on  East  27th  Street  from  Third  to  Madison  Avenues, 
since  which  time  large  areas  of  blocks  of  this  description  have 
been  put  down  with  varying  success,  the  pavement  failing  uni- 
versally under  heavy  travel  and  requiring  renewal  or  extensive 
repairs  in  from  one  to  two  years,  and  revealing  the  fact  that  an 
asphalt  block  pavement  at  least,  as  at  present  constructed,  is 
suitable  only  for  residence  streets  of  the  lightest  travel.  The 
causes  of  this  are  not  far  to  seek  after  a  study  of  the  nature  of 
the  blocks  and  of  the  technology  of  the  industry. 

Asphalt  blocks  consist  of  a  mineral  aggregate  and  a  bituminous 
cementing  material,  as  is  the  case  in  the  sheet  or  monolithic 
asphalt  pavement.  They  differ  essentially  from  the  latter  form 
of  construction  in  that  the  aggregate  is  much  coarser,  containing 
particles  as  large  as  J  or  f  inch  in  size,  while  the  cementing  mate- 
rial is  of  a  much  harder  consistency,  to  enable  the  blocks  to  be 
handled  in  the  course  of  their  transfer  from  the  place  where  they 
are  made  to  the  street  and  to  be  stored  for  some  time  without 
losing  their  shape.  Blocks  of  the  ordinary  surface  mixture  which 
is  used  in  the  construction  of  a  sheet  asphalt  pavement  which 
would  withstand  the  heaviest  travel  could  not  be  transferred  from 
the  plant  to  the  street  without  doing  so,  and  under  a  hot  summer 
sun  would  soon  become  a  monolithic  mass  in  the  street,  even  if 
it  were  possible  to  place  them  there  before  they  were  so  much 
out  of  shape  as  to  make  it  impossible  to  lay  them.  One  of  the  in- 
herent defects  in  asphalt  blocks,  at  least  as  they  have  been  laid 
up  to  the  present  time,  is  that  the  cementing  material  which  binds 
them  together  is  too  hard  to  enable  the  block  to  resist  heavy  travel, 
and  they  have  gone  to  pieces,  especially  in  cold  and  wet  weather, 
after  being  exposed  to  it  for  but  short  periods  of  time.  In  ad- 
dition, the  aggregate  of  an  asphalt  block  is  not  a  satisfactory  one 
as  far  as  grading  is  concerned.  It  consists  to-day  of  crushed 


ASPHALT   BLOCKS. 


391 


trap-rock  or  similar  hard  stone,  which  will  pass  a  screen  having 
openings  f  inch  in  diameter.  Whether  these  screenings  are  made 
particularly  for  the  purpose  with  steel  rolls  or  are  the  finer 
portions  of  stone  which  has  been  crushed  for  concrete,  they  al- 
ways contain  an  excess  of  particles  of  a  size  which  will  pass  a 
screen  of  ten  meshes  to  the  linear  inch,  and  be  retained  on  one  of 
twenty  meshes.  The  screening  of  such  material  does  not  vary 
largely  from  year  to  year,  as  can  be  seen  from  the  following  figures: 


Year. 

1906 

1907 

Passing  200-mesh  screen  

11 

18 

13 

18 

15 

20 

"       100     "         "       

8 

13 

6 

8 

7 

10 

•'         80     "         " 

3 

5 

2 

3 

3 

4 

"         50     "         " 

8 

13 

8 

11 

8 

11 

u         40     "         " 

4 

6 

3 

4 

3 

4 

"         30     "         " 

6 

9 

7 

10 

7 

10 

"         20     "         "       

6 

9 

9 

13 

9 

12 

"         10     "         "      

17 

27 

24 

33 

21 

29 

"           t  ^-inch  mesh  screen 

37 

28 

27 

100 

100 

100 

100 

100 

100 

In  1906  there  was  a  considerably  larger  percentage  of  grit 
than  in  1907,  but  otherwise  the  grading  did  not  differ  essentially. 
If  asphalt  blocks  are,  however,  regarded  as  being  composed  of 
small  particles  of  stone  or  grit,  the  voids  in  which  are  filled  with 
a  standard  mixture  such  as  had  been  found  most  desirable  for 
sheet  asphalt  surfaces,  the  portion  of  the  crushed  trap-rock  which 
plays  the  role  of  sand,  it  will  be  seen  on  calculation,  has  a  grading 
which  is  entirely  "unsuited  for  the  purpose  for  which  it  is  used, 
and  one  which  would  never  be  employed  in  the  sheet  asphalt 
industry.  There  is  no  way  of  modifying  this  grading  except 
by  rejecting  the  excess  of  10-mesh  material,  and  even  then  there 
remains  a  deficiency  in  the  grains  passing  sieves  of  80-  and  100- 
meshes,  while  the  expense  involved  makes  it  quite  impossible 
to  attempt  such  a  modification.  The  crushed  rock  must  be  used 
just  as  it  comes  from  the  rolls  or  from  the  crusher,  and  the  grading 
is  uniformly  bad,  as  can  be  seen  from  the  analyses  of  blocks  made 


392  THE  MODERN  ASPHALT  PAVEMENT. 

by  various  firms  and  corporations.  There  would  be  no  possi- 
bility of  obtaining  good  service  from  a  sheet  asphalt  surface  with 
a  mineral  aggregate  of  such  grading,  and  it  is  not  surprising, 
therefore,  that  asphalt  blocks  do  not  wear  when  subjected  to 
heavy  travel,  especially  as  most  blocks  are  made,  as  has  been 
said,  with  an  asphalt  cement,  which  is  far  too  hard  and  which,  if 
used  in  a  sheet  asphalt  pavement,  would  result  in  scaling  of  the 
surface  during  damp,  cold  weather. 

The  question  at  once  arises  as  to  what  opportunities  are  possible 
for  modifying  and  improving  the  character  of  an  asphalt  block. 
As  a  modification  of  the  grading  of  the  crushed  trap-rock  is  im- 
practicable for  economic  reasons,  if  a  more  satisfactory  mineral 
aggregate  is  to  be  obtained,  recourse  must  be  had  to  materials 
found  in  nature  which  can  be  combined  to  give  the  desired  grad- 
ing, such  as  a  well  graded  sand  or  clean  trap-rock  grit  of  proper 
size  or  gravel.  There  would  be  no  difficulty  in  obtaining  proper 
sands,  such  as  are  used  in  the  sheet  asphalt  industry,  but  suitable 
gravel  would  be  more  difficult  to  find.  An  opportunity,  however, 
is  afforded  for  improving  somewhat  the  character  of  the  block 
in  another  direction,  by  the  use  of  a  more  suitable  asphalt  cement 
than  that  which  has  been  in  use  hitherto,  one  which  is  not  so 
susceptible  to  extremes  of  temperature.  With  such  a  material, 
a  consistency  which  would  be  suitable  for  making  a  block  which 
would  not  be  so  brittle  at  low  temperatures  could  be  used,  and, 
at  the  same  time,  the  block  would  not  be  so  soft  under  a  summer 
sun  as  to  lose  its  shape  on  storage  without  lateral  support  or 
under  pressure  before  being  placed  in  the  street.  Such  a  cement 
is  found  in  one  prepared  from  Gilsonite  and  an  asphaltic  flux.  It 
can  be  used  of  a  much  softer  consistency  than  one  made  with 
Trinidad  or  Bermudez  asphalt  without  danger  of  producing  a 
block  which  will  not  retain  its  shape.  This  can  be  seen  by  a  com- 
parison of  the  consistency  of  the  three  cements,  as  they  are  used  in 
making  blocks,  at  different  tejnperatures. 

Penetration-millimeters. 
32°  F.  77°  F.  110°F. 

Trinidad  asphalt 2  1.4  6.8 

Bermudez  asphalt 2  1.3  7.3 

Gilsonite 5  2.6  7.5 


ASPHALT    EfLOCKS. 


393 


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3    *  2 

8    -S  x 

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f,J 


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—  *^5 

§  x 

£  * 


8   «-   §iM    S 


ao  (N 

..  bC  nH 

^    .s  x 

S    -s  « 

QO       «  X 

HH  CO 


f 

Tt«oo      Oi 


8 


§    |    x 
8   fi    x 

CO 


^         ^ 

^5        CO 

8 


^     °°; 
w     ^! 


^ 


-g      X 

I    x 


'HCOO*OO5 


O5O>        0s- 
^J*  4s*       OJ 

<N(N       00 


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t    t/. 

If. 

§     5 

53     - 


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394  THE  MODERN  ASPHALT  PAVEMENT. 

Under  any  circumstances,  asphalt  blocks  which  are  suitable 
to  resist  heavy  traffic  will  be  sufficiently  soft  to  become,  in  summer, 
almost  a  monolothic  surface  under  travel. 

The  character  of  asphalt  blocks  is  usually  determined  both 
by  chemical  and  physical  tests,  the  latter  being  the  more  important 
and  including  determinations  of  density,  modulus  of  rupture, 
and  loss  from  attrition  in  a  rattler  of  the  type  used  in  testing 
paving  brick.  The  results  of  such  tests  on  various  blocks  produced 
by  the  most  prominent  manufacturers  are  presented  in  the  ac- 
companying table, 

SUMMARY. 

Asphalt  blocks  are  very  satisfactory  under  certain  circum- 
stances as  a  form  of  pavement  for  residence  or  light  traffic  streets, 
but  experience  has  shown  that  such  a  pavement  is  unable  to 
wear  for  any  length  of  time  under  heavy  traffic. 


CHAPTER    XIX. 

THE    PROCESS    OF    COMBINING    THE    CONSTITUENTS    INTO    A 
SURFACE  MIXTURE. 

ASPHALT  cement  of  a  desirable  nature,  a  sand  or  sands  which 
will  afford  a  satisfactory  grading,  and  a  sufficiently  finely  divided 
mineral  matter  for  a  filler  being  available,  it  is  necessary  that 
these  materials  should  be  combined  with  great  care,  skill,  and 
uniformity  in  order  to  produce  a  surface  mixture  which  shall  be 
free  from  criticism. 

To  bring  about  this  combination  some  type  of  plant  is  necessary 
which  shall  make  it  possible  to  meet  the  following  conditions: 

1.  To  feed  a  sand  or  mixture  of  sands  into  the  sand  heater 
with  great  regularity  and  to  have  it  pass  through  the  drum  in 
such  a  way  that  it  is  uniformly  heated  and  the  particles  not  segre- 
gated according  to  size. 

2.  To  raise  the  heated  sand  to  a  temperature  of  from  330° 
to  380°  F.  as  it  emerges  from  the  heater,  without  reducing  its  tem- 
perature essentially,  pass  it  through  a  sieve  which  shall  remove 
all   particles   larger  than   those   passing  a  laboratory  screen   of 
10  meshes  to  the  inch,  and  collect  it  hi  some  form  of  bin  where 
it  can  be  held  for  some  time  without  too  much  radiation  and 
from  which  it  can  be  drawn  without  delivering  at  one  time  a  finer 
and  at  another  tune  a  coarser  material. 

3.  To  have  a  melting-tank  where  asphalt  cement  can  be  main- 
tained in  a  melted  condition  and  at  a  uniform  temperature  and 
provided  with  suitable  means  of  agitation,  either  air  or  steam. 

4.  To  have  suitable  provisions  for  determining  accurately  the 
weight  or  volume  of  the  constituents  entering  into  the  compo- 
sition of  the  surface  mixture. 

395 


396  THE  MODERN  ASPHALT  PAVEMENT. 

5.  To  have  a  mixer  which  shall  make  an  entirely  uniform  and 
homogeneous  combination  of  all  the  constituents  which  go  into  it. 

6.  With  a  satisfactory  plant  it  is  equally  necessary  to  have 
a  foreman  to  run  it  who  not  only  understands  how  to  make  every- 
thing move  uniformly  but  who  has  had  experience  in  and  under- 
stands the  technology  of  the  industry  and  the  reasons  for  each 
step  that  is  taken. 

These  necessities  may  now  be  considered  in  greater  detail. 

Sand. — To  obtain  a  sand  of  satisfactory  grading  it  has  already 
been  shown  that  it  is  usually  necessary  to  mix  two  or  more  sands. 
To  obtain  a  uniform  mixture  from  sands  which  will  give  a  proper 
grading  requires  care  and  attention  and  proper  facilities  for  storing 
the  sand  conveniently  in  the  rear  of  the  sand-drums.  The  two 
or  more  sands  are  then  wheeled  up  or  shovelled  in  separate  piles 
in  the  neighborhood  of  the  bucket  elevators,  which  are  to  elevate 
it  to  the  drums.  The  sands  are  then  fed  into  the  buckets  with  a 
shovel  or  hoe  by  laborers  in  such  proportions  as  may  be  found 
by  experiment  to  be  necessary.  This  feeding  must  be  carefully 
watched,  as,  owing  to  the  class  of  labor  employed,  little  depend- 
ence can  be  placed  upon  the  laborer  himself.  If  the  feeding  is 
irregular  the  surface  mixture  will  also  be  irregular.  The  regu- 
larity of  the  feeding  is  determined  on  the  platform  by  sifting. 

To  obtain  uniformity  in  the  temperature  of  the  sand  the  type 
of  sand-heater  must  be  a  satisfactory  one  and  the  firing  must 
be  as  carefully  done  as  with  a  steam-boiler.  Only  experienced 
firemen  should  be  employed  and  they  should  be  instructed  to 
watch  the  temperature  of  the  effluent  sand  closely. 

The  hot  sand  falls  from  the  drums  into  a  boot,  from  which  it 
is  raised  to  the  sand -screen  over  the  sand-bin.  This  elevator 
should  be  well  closed  in  to  prevent  radiation  and  the  screen  and 
bin  should  also  be  enclosed. 

The  screen  should  be  cylindrical  or  conical  in  shape;  in  the 
latter  case,  3  feet  in  diameter  at  one  end  and  20  inches  at  the 
other.  It  should  revolve  about  12  revolutions  per  minute.  At 
the  end  of  the  larger  diameter  it  is  covered  for  half  of  its  length 
with  cloth  of  10  meshes  to  the  inch,  No.  22  wire.  The  remainder 
should  be  8  meshes  of  No.  18  wire,  the  entire  length  being  5  to  6  feet. 


THE  PROCESS  OF  COMBINATION.  397 

Angle-irons  placed  lengthwise  of  the  screen  at  each  quadrant 
will  strengthen  it  and  increase  its  capacity  by  throwing  the  sand 
about. 

The  sand  should  not  be  allowed  to  fall  into  the  bin  irregu- 
larly and  from  whatever  point  it  passes  the  screen.  It  should 
all  fall  into  a  hopper  which  opens  over  the  centre  of  the  bin.  This 
is  quite  necessary  to  prevent  segregation,  as  otherwise  the  fine 
sand  would  pass  the  screen  first  and  go  to  one  side  of  the  bin, 
the  coarser  particles  collecting  at  the  other. 

'  At  best  a  certain  segregation  results  on  drawing  sand  from 
the  bin.  Unless  the  bin  is  kept  more  than  half  full  there  is  a 
tendency  to  form  a  hollow  cone  in  the  centre  of  the  mass  of  sand, 
down  the  sides  of  which  the  coarse  particles  run  and  accumulate, 
so  that  every  now  and  then  there  is  a  delivery  of  coarse  and  again 
a  delivery  of  fine  sand.  This  can  only  be  avoided  by  not  draw- 
ing the  bin  down  too  low. 

Various  shapes  of  bin  have  been  suggested,  but  a  cylinder 
and  cone  or  a  half  cylinder  and  half  cone  are  probably  the  best. 
The  gate  should  be  in  the  bottom  of  the  cone  and  not  in  the  side. 

Segregation  is,  however,  apt  to  take  place  in  -any  form  of  bin, 
and  that  form  which  prevents  this  to  the  greatest  extent  is  the 
most  desirable. 

The  temperature  at  which  it  is  necessary  to  maintain  the  sand 
in  order  to  produce  a  satisfactory  mixture  will  depend  on  the 
character  of  the  mixture  that  is  being  turned  out,  the  nature 
of  the  asphalt  in  use,  the  weather,  and  the  distance  to  the  street 
from  the  plant.  If  the  mixture  is  a  fine  one,  carrying  much  filler 
and  bitumen,  if  Trinidad  asphalt  is  the  cementing  material,  and 
if  the  weather  is  cool,  385°  F.  is  not  too  high  a  temperature  for 
the  sand  in  the  bin.  If  a  smaller  amount  of  filler  is  employed 
the  temperature  need  not  exceed  335°.  In  any  case  the  mixture 
should  reach  the  street  at  such  a  temperature  that  it  can  be  raked 
freely.  In  the  best  New  York  mixtures  the  temperatures  aver- 
age 330°  F.  The  average  mixture  of  the  country  will  reach  the 
street  at  310°.  The  above  applies  to  a  standard  Trinidad  mix- 
ture. If  other  asphalts  are  used  the  temperatures  must  be  con- 
siderably reduced,  as  they  will  suffer  from  such  heat.  The  harden- 


398  THE  MODERN  ASPHALT  PAVEMENT. 

ing  effect  of  hot  sand  on  asphalt  cement  has  already  been  noted, 
and  should  always  be  allowed  for  in  those  mixtures  made  with 
susceptible  bitumens  such  as  Bermudez  and  the  hard  residues 
from  petroleums  or  where  the  flux  in  use  is  one  carrying  much 
volatile  oil. 

Melting-tanks. — The  melting-tanks  in  which  the  asphalt  cement 
is  made  at  the  smaller  plants  or  into  which  it  is  drawn  from  the 
refining-tanks  at  the  larger  ones  should  be  so  constructed  that 
no  portion  of  their  contents  shall  become  readily  overheated. 
The  bottoms  should  be  protected  from  direct  flame  by  a  fire- 
brick arch.  Agitation  is  necessary,  not  only  with  such  an  asphalt 
as  Trinidad,  for  the  purpose  of  keeping  the  mineral  matter  in  sus- 
pension, but  with  others  as  well,  to  keep  the  material  from  too 
long  contact  with  the  sides  of  the  tank,  and  of  even  temperature, 
since  convection  in  melted  asphalt  results  in  but  a  very  slow 
motion  of  the  mass. 

Agitation  with  steam  is  undoubtedly  the  best  method,  as  the 
action  of  air  on  all  oils  at  a  high  temperature  is  very  strong,  the 
result  of  blowing  an  asphaltic  residuum  at  a  temperature  of  350° 
with  air  for  twenty-four  hours  being  to  convert  it  into  a  semi- 
solid  buttery  mass. 

Agitation  is  also  a  matter  of  economy  as  far  as  the  life  of  the 
tanks  themselves  are  concerned,  as  they  will  burn  out  very  rapidly 
if  sediment  or  coke  is  allowed  to  collect  in  them. 

In  plants  where  a  large  amount  of  work  is  done  some  pro- 
vision in  the  form  of  a  pneumatic  lift  should  be  made  for  raising 
the  cement  to  the  asphalt  bucket,  where  it  is  gauged  or  weighed 
without  the  aid  of  manual  labor. 

The  requisite  amount  of  asphalt  should  be  weighed  and  not 
measured  and  the  same  may  be  said  of  the  sand.  The  same  volume 
of  sand  may  vary  very  much  in  weight  according  to  the  way  it 
runs  into  the  receptacle. 

The  type  of  mixer  in  use  in  combining  the  constituents  is, 
of  course,  of  importance  and  still  more  so  the  way  in  which  it  is 
kept  in  repair  and  good  order.  It  is  usually  constructed  to  mix 
a  volume  of  9  cubic  feet  at  one  operation,  but  as  large  a  volume  as 
18  can  be  thoroughly  mixed  in  a  properly  constructed  mill  and 


THE  PROCESS  OF  COMBINATION.  399 

corresponding  economy  attained.  The  mixer  should  be  pro- 
vided with  a  liner  which  can  be  renewed  when  worn.  It  should 
be  provided  with  a  set  of  teeth  made  of  chilled  iron  or  having 
steel  tips  which  reach  within  a  quarter  of  an  inch  of  the  lining. 
The  teeth  should  be  set  on  a  shaft  the  bearings  of  which  can  be 
raised  or  lowered  by  the  introduction  or  removal  of  shims  so  as 
to  bring  the  teeth  nearer  or  farther  away  from  the  liner.  It  should 
have  a  gate  which  is  tight  and  will  prevent  the  leaking  of  either 
asphalt  or  sand.  In  the  larger  types  of  mixer  the  gate  is  controlled 
by  some  power  appliance. 

The  mixer  rests  on  what  is  technically  known  as  the  platform, 
which  is  sufficiently  elevated  to  admit  a  truck  beneath.  Behind 
the  mixer  is  the  sand-box  in  which  the  sand  and  filler  are  weighed 
or  measured  out.  Over  it  is  the  bucket  for  the  asphalt  cement 
suspended  from  a  scale.  The  sand  and  filler  having  been  weighed 
in  the  box  and  the  A.  C.,  the  technical  designation  of  the  asphalt 
cement,  in  the  bucket,  the  two  former  are  allowed  to  run  out 
through  a  gate  into  the  covered  mixer,  which  is,  of  course,  in  motion, 
or  if  the  sand-box  is  one  that  has  no  gate,  it  is  dumped  into  the 
mixer.  It  is  allowed  to  remain  there  for  from  15  to  20  seconds  to 
mix  the  dry  materials  thoroughly.  The  asphalt  cement  is  then 
poured  or  run  directly  into  the  middle  of  the  dry  mix  and  not  spread 
about  over  different  parts  of  it,  as  the  mixer  teeth  will  bring  all  the 
sand  to  the  centre  to  meet  the  bitumen,  but  will  not  be  able  to  do  so 
as  readily  with  the  latter.  After  the  introduction  of  the  asphalt 
cement  the  mixing  is  continued  for  about  one  hundred  revolutions. 
The  gate  to  the  mixer  is  then  opened  and  the  mixture  dropped 
into  the  truck. 

Where  the  platform  is  large  enough  a  testing-room  should  be 
provided  there  for  the  use  of  the  yard  foreman;  otherwise  it 
should  be  upon  the  ground  in  front  of  the  mixer,  as  in  the  case  of 
a  railroad  plant.  He  should  have  there  a  set  of  sand-screens, 
a  sand-balance,  a  flow  outfit  for  controlling  the  consistency  of  his 
A.  C.  and  manilla  paper  for  making  pat  tests  of  his  mixture.  He 
should  screen  samples  of  sand  taken  from  the  boot  of  the  sand- 
drums  and  from  the  bin  in  order  to  be  sure  that  the  sand  mixture 
is  being  fed  in  the  proper  proportions  and  evenly.  He  should 


400  THE  MODERN   ASPHALT  PAVEMENT. 

make  comparative  flow  tests  of  the  asphalt  cement  he  has  in  use 
with  that  of  the  standard  furnished  him  for  the  purpose.  Finally, 
he  should  make  frequent  pats  of  his  mixture  to  determine  whether 
it  is  carrying  a  proper  amount  of  A.  C.  and  whether  it  is  properly 
balanced.  These  points  are  recognized  by  the  stain  made  by 
the  bitumen  on  the  paper  and  by  the  appearance  of  the  surface 
of  the  hot  pat  when  it  is  held  on  a  level  with  the  eye.  Experi- 
ence is,  of  course,  required  to  interpret  these  latter  tests  and  to 
understand  the  indications  which  are  afforded.  In  addition 
such  samples  should  be  taken  on  the  platform  as  are  needed  for 
examination  in  the  laboratory  by  more  accurate  methods. 

The  Production  of  Binder. — Binder  is  turned  out  in  exactly 
the  same  way  as  the  surface  mixture  except  that  the  tempera- 
ture and  not  the  grading  of  the  stone  is  to  be  watched  and  the 
mixing  is  done  in  a  mixer  having  fewer  and  shorter  teeth.  The 
temperature  of  the  binder  can  be  appreciably  lower  than  that 
of  the  surface.  It  should  certainly  not  be  so  hot  as  to  cause  the 
asphalt  to  run  off  the  stone,  as  in  that  case  it  will  reach  the  street 
without  sufficient  cementing  material  to  hold  it  together,  a  result 
often  noticed  in  careless  work. 

Types  of  Plants  and  Machinery. — In  the  preceding  pages  no 
mention  has  been  made  of  any  particular  type  of  plant  or  machinery, 
as  this  seemed  unnecessary.  It  is  the  results  obtained  and  the 
way  in  which  they  are  attained  which  are  of  the  greatest  interest 
to  the  engineer  and  to  the  private  individual  to  whom  this  book 
is  addressed.  One  type  may  do  slightly  more  economical  work 
than  another  or  slightly  better.  If  the  latter  is  true  it  can  be 
better  judged  from  the  character  of  the  material  turned  out  or 
from  the  celerity  with  which  the  work  is  accomplished. 

It  will  be  of  interest  here,  however,  to  describe  the  type  of 
the  machinery  which  the  author  has  found  most  satisfactory. 

Permanent  Plants. — In  large  cities  where  a  very  considerable 
amount  of  work  is  done  every  year  a  permanent  plant  will,  of  course, 
be  established,  consisting  of  proper  storage,  for  two  or  more 
grades  of  sand,  in  the  shape  of  bins,  which  can  be  readily  and 
economically  filled  from  the  boats,  cars,  or  other  means  of  trans- 
portation which  supply  the  sand.  This  material  should  natu- 


THE  PROCESS  OF  COMBINATION.  401 


i 


rally  be  handled,  for  economy's  sake,  as  far  as  possible  by  power 
and  the  bins  should  be  so  placed  in  relation  to  the  sand-heaters 
that  as  little  labor  as  possible  will  be  necessary  to  feed  the  sand 
to  the  heaters. 

Sand-heaters. — The  sand  used  in  different  localities  varies 
from  dry  bank  to  dripping-wet  river  sand,  and  the  heater  is  required 
to  drive  off  the  moisture  and  heat  to  a  temperature  of  330°  F. 
or  over  the  maximum  amount  of  sand  per  unit  of  time  with  the 
minimum  amount  of  fuel.  As  the  result  of  actual  trial  of  many 
different  designs  the  Iroquois  Iron  Works  has  adopted  a  setting 
of  two  horizontal  revolving  drums,  fired  with  induced  draft,  as 
giving  the  greatest  efficiency.  By  the  proportioning  of  the  size 
of  the  drum,  furnace,  and  induced  draft,  all  the  available  heating 
power  is  obtained,  and  by  heavy  construction  and  perfection  of 
details  the  durability  of  the  machine  is  assured. 

The  drum-shells  are  made  of  j"  steel  plate  20  feet  long  rolled 
to  a  40"  diameter  circle,  and  are  riveted  together  with  two  hori- 
zontal butt-strap  joints.  These  shells  are  carried  at  both  ends 
by  heavy  cast-iron  spiders.  Shafts  from  these  spiders  extend 
out  beyond  the  shells  and  form  the  journals.  The  bearing  at  the 
hot  sand  end  takes  the  thrust,  being  grooved  similar  to  a  propeller 
shaft-bearing.  The  bearing  boxes  are  fitted  with  trunnions  allow- 
ing swinging  in  a  vertical  plane.  The  trunnions  rest  on  swivel 
brackets,  permitting  swinging  in  a  horizontal  plane;  consequently 
there  can  be  no  binding  in  the  boxes,  they  being  able  to  align 
themselves  at  all  tunes,  a  necessary  qualification  for  a  drum  revolv- 
ing in  a  furnace.  Sheet-steel  shelves  are  riveted  the  entire  length 
of  the  ulterior,  which  give  additional  heating  surface  and  at  the 
same  time  are  continually  lifting  the  sand  and  allowing  it  to  fall 
through  the  diameter  of  the  drum.  The  grates  are  located  directly 
under  the  cold  sand  end  of  the  drum-shells. 

By  means  of  a  fan  the  combustion  gases  are  drawn  along  under 
and  back  through  the  drums,  coming  in  contact  with  the  sand, 
which,  by  the  shelves  on  the  interior  of  the  drums,  is  distributed 
through  them.  By  this  method  the  surfaces  of  the  drum  are 
heated  by  direct  radiation  from  the  gases  of  combustion,  and  the 
gases,  being  drawn  through  the  drum  and  coming  in  intimate 


402  THE  MODERN  ASPHALT  PAVEMENT. 

contact  with  the  particles  of  sand,  not  only  draw  off  the  released 
moisture  and  discharge  it  outside  the  setting  but  also  assist  in 
heating  the  sand  to  the  required  temperature.  This  induced 
draft  is  a  valuable  feature  and,  as  it  is  easily  regulated,  increases 
the  capacity  and  ensures  obtaining  the  maximum  calorific  value 
from  the  fuel.  Such  a  sand-heater  is  illustrated  in  Fig.  17. 

These  drying  cylinders  are  mounted  in  a  brick  or  steel-plate 
setting,  as  desired.  For  permanent  installation  the  brick  setting 
is  preferred.  The  steel-plate  setting  is  well  shown  in  the  illustra- 
tion, Fig.  17,  from  which  it  will  be  seen  that  the  bearing  boxes 
supporting  the  cylinders  are  mounted  on  a  built-up  framework 
at  both  hot  and  cold  sand  ends.  This  framework  consists  of  a 
base  of  riveted  channels  and  steel  plate,  upon  which  is  mounted 
cast-iron  brackets  for  carrying  the  bearing  boxes.  The  sides  are 
made  of  J"  steel  plate  reinforced  with  angles.  The  roof  consists  of 
two  steel  plates.  The  inner,  which  is  \"  thick,  is  curved  to  con- 
form to  the  arc  of  the  drums,  thus  holding  the  heat  against  the 
latter.  The  outer  covering  of  medium  gauge  sheet  steel  is  carried 
straight  across  to  form  a  rain-shed.  The  inner  and  outer  covers 
are  riveted  to  a  trussed  angle-iron  frame  which  is  absolutely  self- 
supporting.  The  sides,  ends,  and  roof  are  made  in  sections  and 
bolted  together,  permitting  the  entire  setting  to  be  dismantled 
into  small  units  which  are  easily  handled  and  packed  for  ship- 
ment. For  the  protection  of  the  steel  plate  it  is  customary  to 
lay  up  a  lining  of  one  thickness  of  fire-brick  at  the  sides  extending 
two-thirds  the  length  of  the  setting.  The  exhaust-fan  is  mounted 
on  a  timber  frame  to  one  side  and  can  discharge  into  the  air  or 
be  connected  with  a  dust-collector,  as  may  be  preferred. 

The  drums  discharge  into  a  boot,  from  whence  the  hot  sand 
is  elevated  by  means  of  steel  buckets  on  a  steel  pin  chain  to  a 
rotary  screen  covered  with  cloth  of  the  dimensions  which  have 
been  described.1  The  screen  discharges  into  a  steel  storage-bin 
of  from  6  to  9  cubic  yards  capacity.  From  the  storage-bin  it 
flows  by  gravity  to  a  triangular-shaped  weighing-box  mounted 
on  a  beam-scale.  Here  the  required  amount  of  stone  dust  is 

1  See  page  396, 


=fc         "3 


•a 

j 


404  THE  MODERN  ASPHALT  PAVEMENT. 

added  and  the  charge  brought  up  to  accurate  weight  ready  for 
the  mixture. 

Melting-tanks. — For  melting  the  asphalt  two  types  of  kettle 
are  used,  fire  and  steam.  The  fire  melting-tanks  are  either  cylin- 
drical or  rectangular,  with  semicircular  bottom,  and  are  set  in 
the  furnace  with  a  fire-brick  arch  between  the  grates  and  the  bot- 
tom of  the  tank  to  prevent  too  rapid  heating,  which  would  tend 
to  coke  the  material  on  the  bottom.  The  fire  melting-tanks  are 
now  more  generally  used  for  small  portable  plants  in  small  units 
of  4  tons  capacity.  For  larger  and  more  permanent  plants  the 
steam  melting-tanks  are  preferable. 

The  steam  melting-tanks  are  rectangular  in  shape,  contain- 
ing horizontal  oval-shaped  coils  of  1J"  pipe.  Fig.  18.  One 
hundred  and  twenty-five  pounds  steam  pressure  is  generally 
used,  which  gives  a  temperature  in  the  coil  of  345°  F.  Agitation 
is  accomplished  in  both  fire  and  steam  melting-tanks  by  hori- 
zontal pipes  laid  at  the  bottom,  with  small  perforations.  To 
these  pipes  are  deliverd  either  steam  at  boiler  pressure  or  air 
at  about  20  pounds  pressure.  When  the  asphalt  is  melted  in 
these  kettles  it  is  reduced  with  the  required  amount  of  warm 
flux,  which  is  measured  in  a  special  measuring-tank  and  flows 
by  gravity  to  the  melting-kettles.  The  asphalt  cement  result- 
ing is  now  ready  for  the  mixer  and  is  delivered  to  it  in  one  of  three 
ways :  In  small  semi-portable  plants  a  bucket  carried  by  a  traveller 
mounted  on  wheels  on  a  track  is  run  out  from  the  mixer  over 
the  melting-kettles  and  the  cement  dipped  into  the  bucket.  In 
many  permanent  plants  the  melting-kettles  are  mounted  on  a 
structure  sufficiently  high  for  the  asphalt  cement  to  flow  by  gravity 
directly  into  the  bucket.  The  third  and  very  largely  used 
method  is  setting  a  pneumatic  lift  just  below  the  bottom  of  the 
kettles.  This  pneumatic  lift  consists  of  a  steam-jacketed  steel 
cylinder  fitted  with  inlet-  and  discharge-pipe,  air-pipe,  and  a  system 
of  valves  whereby  the  cement  flows  into  the  lift  from  the  kettles 
by  gravity,  and  by  the  operation  of  suitable  air- valves,  air-pres- 
sure, which  need  not  be  over  5  pounds  and  is  generally  the  same 
as  the  agitation  pressure,  is  admitted  on  top  of  the  cement,  thereby 
automatically  closing  the  valve  in  the  intake  and  forcing  the 


FIG,  18.— Steam  Melting  Tank. 


405 


406  THE  MODERN  ASPHALT  PAVEMENT. 

cement  up  through  the  discharge-pipe  to  the  weighing-bucket 
at  the  mixer. 

Mixer. — The  mixer  consists  of  a  rectangular-shaped  steel  shell 
with  semicircular  bottom,  containing  two  horizontal  square 
shafts,  upon  which  shafts  are  bolted  blades,  or  teeth,  as  they  are 
commonly  called.  Fig.  20.  These  shafts  are  made  to  revolve 
by  gearing  at  a  speed  of  from  60  to  75  revolutions.  The  teeth 
are  made  in  two  different  shapes,  called  right  and  left  hand,  and 
are  so  set  upon  the  shafts  that  they  work  the  material  horizontally 
towards  the  centre,  and  at  the  same  time  are  continually  tossing 
it  vertically.  The  result  is  that  an  absolutely  homogeneous 
mixture  of  the  sand  and  asphalt  cement  is  obtained  within  a 
minute  and  a  half,  when  the  mixer-man  pulls  a  lever,  opening 
the  slide  in  the  bottom,  and  the  finished  topping  is  discharged 
into  the  wagon  ready  for  hauling  to  the  street. 

Where  a  plant  has  but  one  mixer  for  turning  out  both  sur- 
face mixture  and  binder  it  is  provided  with  another  shaft  for 
carrying  shorter  teeth  at  much  wider  intervals.  This  shaft  re- 
places the  one  used  for  surface  mixture  when  binder  is  to  be  pro- 
duced. 

Portable  or  Semi-portable  Plants. — In  cities  where  work  is 
only  done  at  intervals  and  where  the  amount  is  not  sufficiently 
great  to  justify  the  construction  of  a  permanent  plant,  portable 
or  semi-portable  plants  are  used. 

The  first  type  of  portable  plant  consisted  of  two  railroad  flat 
cars,  one  to  carry  the  boiler  and  melting  tanks  and  the  other  for  the 
sand  heaters,  with  the  mixing  platform  between  the  cars  when 
the  plant  was  set  up  for  use.  Such  a  plant  is  illustrated  in  Fig. 
21.  The  cost  of  setting  up  and  taking  down  this  form  of 
plant  when  moving  from  place  to  place  was  rather  large.  The 
plant  has  therefore  been  modified  to  occupy  a  single  car,  render- 
ing the  cost  of  putting  it  in  operation  extremely  small.  A  plant 
of  this  type,  as  manufactured  by  the  Iroquois  Iron  Works,  is 
shown  in  Fig.  19. 

The  semi-portable  plant  is  one  which  is  readily  taken  down 
and  erected,  but  is  not  fixed  upon  a  car.  It  consists  of  a  steel 
tower  with  mixer  platform,  as  illustrated  in  Fig.  22,  which  is 
accompanied  by  the  necessary  melting-tanks,  usually  heated 


THE    PROCESS    OF    COMBINATION. 


407 


by  fire.     This  type  of  plant  has  been  found  very  successful  in 

late  years  and  has  a  large  future  before  it  for  work  in  small  towns. 

Plants  of  the  two  previous  types  require  skilled  handling  and 

close  attention,  but  with  a  good  foreman  and  engineer  equally 


FIG.  19. 

good  work  can  be  turned  out  from  them  as  from  a  permanent  plant, 
and  they  are  highly  recommended  by  the  author. 

Bituminous  Concrete  Plant. — For  the  production  of  bitu- 
minous concrete  any  of  the  previous  types  of  plant  will  serve,  if 
the  screen  over  which  the  heated  material  passes  is  arranged  so 
as  to  separate  the  heated  mineral  matter  into  three  sizes,  sand, 
fine  stone  passing  openings  f  inch  in  diameter,  and  coarse  stone 
up  to  f  inch  in  size,  and  if  the  bin  is  divided  into  compartments 
to  hold  these  separate  grades.  A  special  form  of  plant  is  not 
required  for  this  purpose,  nor  is  it  necessary  to  separate  the  stone 
into  more  than  three  sizes,  as  has  been  shown  by  the  successful 
work  done  in  this  way  as  long  ago  as  1896. 


a 

OJ 

I 


. 


I 


FIG.  22.-  Semi-portable  Mixing  Platform 


410 


THE    PROCESS    OF    COMBINATION.  411 


SUMMARY. 


This  chapter  describes  the  process  of  combining  the  con- 
stituents into  a  surface  mixture,  including  the  machinery  and 
plant  necessary  for  heating  the  sand  and  mixing  the  hot  min- 
eral aggregate  with  asphalt  and  the  type  of  tanks  necessary  for 
melting  the  latter. 


PART  V. 

HANDLING  OF  BINDER  AND  SURFACE  MIXTURE 
ON  THE  STREET. 


CHAPTER  XX. 
THE  STREET. 

Transportation  of  the  Materials  to  the  Street. — The  transpor- 
tation of  the  binder  and  surface  mixture  from  the  plant  to  the 
point  where  the  pavement  is  being  constructed  is  something  that 
cannot  be  undertaken  carelessly  and  with  no  other  thought  than 
merely  getting  it  there.  In  the  case  of  the  binder  the  only  con- 
sideration is  that  it  be  so  protected  that  it  will  not  become  cold. 
The  condition  of  the  surface  mixture  when  it  reaches  the  street 
is  much  more  influenced  by  the  conditions  to  which  it  has  been 
subjected  en  route.  In  the  early  days  of  the  industry,  in  Washing- 
ton, D.  C.,  for  instance,  the  old-fashioned  dump-cart,  holding 
from  18  to  27  cubic  feet,  was  in  use.  Aside  from  a  matter  of 
economy,  this  is  the  ideal  way  to  haul  the  material.  Later  on, 
as  the  size  of  the  mixer  was  increased  in  the  larger  cities,  trucks 
were  employed  which  would  hold  six  batches  of  18  cubic  feet, 
or  six  tons.  It  was  soon  found  that  this  method  of  transporta- 
tion was  unsatisfactory,  as  the  larger  mass  of  surface  mixture, 
during  the  long  hauls  which  are  unavoidable  in  cities  of  the  size 
of  New  York  and  the  constant  jarring  over  rough  pavements, 
became  so  compacted  that  it  was  difficult  to  break  it  up  after 
it  was  dumped  on  the  street,  especially  if  the  mixture  was  a  dense 
one  carrying  a  large  percentage  of  filler  and  asphalt  cement.  To 

412 


THE    STREET.  413 

offset  this  disadvantage,  however,  the  larger  mass  loses  heat  much 
less  rapidly  than  is  the  case  with  the  smaller  load,  and  this  is  a 
distinct  gain  in  cold  weather  and  for  repair  work.  A  medium 
course  is,  therefore,  now  pursued  and  loads  of  about  four  tons 
are  hauled. 

In  the  smaller  cities  and  towns  the  question  is  often  a  serious 
one,  as  the  trucks  available  locallyare  often  not  suitable  for  hauling 
surface  mixture.  The  worst  type  is  the  ordinary  dirt  truck  which 
dumps  by  turning  over  slats  which  form  the  bottom  of  the  truck. 
This  truck  does  not  protect  the  mixture  from  cooling  rapidly,  and 
in  dumping  the  entire  mass  is  so  loosened  up  as  to  be  still  further 
cooled,  while  much  of  the  material  is  lost  by  being  carried  away 
on  the  running-gear. 

Whatever  the  form  which  the  load  may  take,  the  surface  should 
be  protected  from  the  air,  at  all  seasons  of  the  year,  by  tarpaulins. 
The  loss  hi  temperature,  if  the  protection  is  suitable,  will  not 
exceed  10°  from  plant  to  street  hi  two  hours,  or  often  after  longer 
intervals,  in  warm  weather. 

It  has  been  found  possible  to  transport  large  masses  of  hot 
surface  mixture  by  rail  or  by  scow  for  long  distances.  As  an  example 
of  this  may  be  cited  work  done  in  New  Rochelle,  N.  Y.,  in  1899. 
Three  hundred  tons  of  mixture  w ere  placed  on  a  scow  at  Long 
Island  City,  N.  Y.,  and  taken  by  a  tug  to  the  point  where  the  sur- 
face was  to  be  laid.  Owing  to  the  inclement  weather  it  was  impos- 
sible to  place  the  material  for  thirty  hours,  but  the  majority  of 
it  was  in  good  condition  to  be  laid  at  that  time  after  the  outer 
cooled  portions  had  been  removed.  The  asphalt  pavement  laid 
in  this  way  has  been  entirely  satisfactory. 

Construction  Work  on  the  Street. — Of  the  work  of  construction 
of  an  asphalt  pavement  on  the  street  consideration  need  be  given 
only  to  that  portion  above  the  base,  that  of  the  latter  involving 
no  principles  which  have  not  already  been  exploited.  In  earlier 
pages  the  desirable  characteristics  of  a  base  have  been  shown, 
and  it  is  here  assumed  that  the  bituminous  surface  is  to  be  applied 
to  such  a  base. 

The  Binder  Course. — In  general  a  binder  course  is  the  first 
applied.  In  the  description  of  the  preparation  of  the  binder 


414  THE    MODERN    ASPHALT    PAVEMENT. 

it  appeared  that  it  was  sent  to  the  street  at  a  temperature  some- 
what lower  than  that  of  the  surface  mixture.  Arriving  there  it 
should  be  dumped  sufficiently  distant  from  the  point  where  the 
spreading  is  to  be  begun  or  from  the  point  where  the  previous 
load  ended  to  permit  of  turning  all  the  material  over  without 
finding  it  necessary  to  finally  distribute  any  of  the  binder  over 
the  base  at  the  point  where  it  has  been  dumped.  This  is  quite 
necessary,  although  not  as  much  so  as  in  the  case  of  surface  mixture, 
to  permit  of  spreading  the  binder  course  evenly,  that  portion 
lying  at  the  point  where  the  load  was  dumped  being  consider- 
ably compressed  by  the  fall  and  the  weight  of  the  incumbent 
mass,  so  that  were  this  not  shovelled  over  the  thickness  at  this 
point  would  be  greater  than  elsewhere  in  the  street. 

The  surface  of  the  load  of  binder  should  be  bright  and  glossy, 
as  should  the  whole  mass  after  it  has  been  dumped.  On  the 
other  hand,  there  should  be  no  excess  of  bitumen,  as  evidenced 
by  asphalt  running  from  the  bottom  of  the  truck  or  by  too  great 
richness  of  the  bottom  of  the  load.  Too  hot  stone  may  cause 
the  bitumen  to  run  off  the  binder.  One  should  not  be  misled 
by  such  an  occurrence  into  the  belief  that  the  load  is  too  rich. 
In  such  a  case,  however,  the  surface  of  the  load  will  generally 
be  dead.  Unless  the  stone  is  covered  with  a  bright  coat  of 
bitumen  the  binder  will  have  no  coherence  and  should  be  re- 
jected. 

The  binder  is  spread  with  rakes  with  long  tines.  It  may  be 
allowed  to  cool  to  a  very  considerable  degree  before  rolling.  If 
rolled  too  hot  it  will  be  much  more  liable  to  displacement  and 
to  being  picked  up  by  the  roller.  It  should  be  rolled  directly 
with  a  steam-roller  weighing  from  five  to  seven  tons. 

Immediately  after  rolling  it  is  ready  for  the  application  of 
the  surface.  If  the  surface  is  not  applied  at  once  the  binder 
should  be  protected  from  becoming  soiled  by  traffic  or  otherwise. 
A  slight  coating  of  dust  will  do  no  harm.  The  hauling  of  a 
sufficient  amount  of  surface  mixture  over  it  to  cover  it  should  not 
break  it  up.  If  this  happens,  except  on  a  weak  base,  it  is  a  sign 
that  it  is  not  of  the  best  quality. 

Too  often  the  thickness  of  binder  specified  is  too  small,  and 


THE    STREET.  415 

in  this  case  it  is  impossible  to  lay  it  so  that  it  will  not  break  up 
to  a  certain  degree  in  putting  on  the  surface.  An  inch  of  binder 
is  never  satisfactory.  Binder  is  composed  of  stone  the  larger 
particles  of  which  are  at  least  an  inch  in  diameter.  It  is  readily 
seen  that  no  satisfactory  bond  of  such  materials  can  be  obtained 
in  such  a  thickness. 

Where  an  asphaltic  concrete  course  is  substituted  for  an  open 
binder  this  must  be  spread  with  shovels  and  the  back  of  the  rake. 
The  tines  should  not  be  used  at  all,  since  they  have  a  tendency 
to  pull  the  larger  stones  to  the  surface  and  cause  a  segregation  of 
the  material. 

The  Surface  Course. — The  mixture  which  is  to  form  the  sur- 
face should  arrive  upon  the  street  at  a  temperature  which  cannot 
be  denned  in  degrees  of  the  thermometer.  It  should  be  hot  enough 
to  work  freely  under  the  rake  if  it  has  a  properly  balanced  mineral 
aggregate,  but  in  no  case  should  exceed  in  temperature  one  which 
the  particular  asphalt  cement  can  resist  without  being  too  much 
hardened,  especially  in  the  mixer  when  being  violently  agitated 
with  hot  sand  in  contact  with  ah*.  As  different  asphalts  are  very 
variable  in  respect  to  their  volatility  and  stability,  the  extreme 
temperature  to  which  mixtures  made  with  them  may  be  heated 
is  quite  different.  This  has  already  been  shown  on  previous 
pages.  The  temperature  will  also  vary  with  the  character  of 
the  mineral  aggregate.  A  dense  mixture  may  be  heated  much 
hotter  without  injury  than  an  open  one.  As  a  general  rule,  it 
may  be  laid  down  that  some  dense  Trinidad  mixtures,  such  as 
that  made  with  a  Portland-cement  filler,  may  with  safety  be  raised 
to  a  temperature  of  340°  to  350°,  if  it  is  necessary,  in  cold  weather. 
By  this  it  is  not  meant  that  such  a  temperature  is  desirable  if 
the  mixture  can  be  worked  at  a  lower  one,  but  that  no  danger 
will  be  incurred  by  its  use  which  is  commensurate  with  the  dis- 
advantages arising  from  inability  to  handle  a  cold  mixture  on 
the  street  and  consequent  poor  workmanship. 

A  Bermudez  mixture  hardens  rapidly  at  temperatures  above 
300°  and  should  not  be  heated  above  that  point  unless  provision 
is  made  for  the  resulting  hardening  by  making  the  asphalt  cement 
about  ten  points  too  soft.  The  same  may  be  said  of  those  asphalts 


416  THE    MODERN    ASPHALT    PAVEMENT. 

which  resemble  Bermudez,  Mexican,  western  Venezuelan,  and 
the  like.  The  best  oil  asphalts  will  resist  high  temperatures  well, 
but  mixtures  made  with  them  do  not  require  to  be  very  hot,  as 
bitumen  of  this  character  is  so  liquid  at  a  comparatively  low  heat 
that  no  difficulty  is  experienced  in  working  them,  even  the  densest, 
at  280°. 

As  a  general  rule,  it  may  be  laid  down  that  the  following  tem- 
peratures may  be  considered  normal  on  the  street: 

Trinidad  asphalt: 

Dense  mixture 325°  F.  to  340°  F. 

Average    "      300°  F.  "  325°  F. 

Open         "      280°  F.  "  300°  F. 

Bermudez  asphalt: 

All  mixtures 280°  F.  "  300°  F. 

The  lowest  temperature  at  which  a  mixture  may  reach  the 
street  and  still  be  considered  satisfactory  is  that  at  which  it  may 
be  raked  to  a  proper  grade  without  too  much  difficulty. 

The  character  of  a  mixture  can  be  judged,  to  a  very  considera- 
ble degree,  by  the  appearance  of  its  surface  in  the  truck  as  it 
comes  upon  the  street,  if  the  haul  has  extended  for  any  distance, 
and  by  its  cohesion  when  it  is  dumped.  The  best  mixture,  carry- 
ing plenty  of  filler,  should  have,  before  dumping,  a  nearly  level 
and  rather  bright  surface.  If  the  material  stands  up  in  a  heap 
as  it  was  dropped  from  the  mixer  it  is  not  rich  enough.  If  it 
tumbles  to  pieces  on  dumping,  it  does  not  contain  enough  filler. 
The  best  mixtures,  which  are  the  only  ones  suitable  for  heavy- 
traffic  streets,  should  stand  up  and  show  in  part  the  shape  of 
the  truck  from  which  they  have  been  dumped. 

This  applies,  however,  only  to  the  natural  asphalts.  The 
residual  asphalts  from  asphaltic  petroleums  become  so  liquid 
at  temperatures  at  which  surface  mixtures  are  handled  that  the 
latter  are  quite  sloppy. 

A  load  of  surface  mixture,  for  the  same  reasons  as  in  the  case 
of  binder,  only  more  emphatically  so,  should  be  dumped  upon 
the  binder  so  far  from  the  material  previously  raked  out  that 
it  will  be  possible  and  necessary  to  shovel  it  all  over  in  order  to 
get  it  in  place.  This  is  most  important,  and  care  in  this  direction 
is  often  lacking.  If  the  mixture  at  the  point  where  the  load  is 


THE    STREET.  417 

dumped  is  not  shovelled  over,  but  merely  brought  to  grade  before 
rolling,  there  will  be  an  excess  of  mixture  at  that  point  which  will 
not  compress  as  much  under  the  steam-roller  as  the  neighboring 
surface,  with  the  result  that  after  the  street  has  been  subjected 
to  traffic  for  some  time  that  part  is  higher  than  the  rest. 

The  surface  mixture  is  distributed  with  hot  shovels  from  the 
point  where  it  has  been  dumped  to  the  place  where  it  is  to  be 
raked  out  to  the  proper  thickness  for  compression.  This  opera- 
tion should  not  be  conducted  too  rapidly.  No  more  should  be 
spread  than  the  rakers  can  handle.  If  it  is  spread  too  rapidly 
the  rakers  will  find  it  necessary  to  step  in  it  in  correcting  inequali- 
ties of  grade,  thus  compressing  the  part  where  their  feet  fall.  This 
depression  they  afterward  fill  with  more  mixture  and  therefore 
leave  at  that  point  more  than  there  should  be.  After  the  street 
is  opened  for  traffic  this  part  of  the  surface  does  not  yield  as  much 
to  final  compression  as  the  remainder  and  the  result  is  an  uneven 
and  bumpy  grade  which  is  accentuated  with  the  lapse  of  time 
and  aids  in  the  disintegration  of  the  pavement  from  the  blows 
of  wheels  bounding  from  the  elevated  spot  to  the  adjoining  sur- 
face. Rakers  should  on  no  account  be  allowed  to  place  their 
feet  on  the  uncompressed  surface  mixture.  If  absolute  necessity 
arise  the  depression  should  not  be  refilled. 

The  mixture  after  it  is  spread  should  be  thoroughly  raked 
out  with  rakes  having  long  and  strong  tines  which  will  penetrate 
through  its  entire  depth.  It  is  necessary,  in  order  to  obtain  a 
regular  surface  to  the  finished  street,  that  all  the  hot  mixture 
shall  be  broken  up  to  a  uniform  state  of  looseness.  None  of  the 
material  in  the  state  of  compression  which  it  has  acquired  in  the 
truck  during  the  haul  to  the  street  should  be  allowed  to  remain 
in  lumpy  form.  If  lumps  remain  in  the  loose  hot  material  the 
effect  will  be  the  same  as  that  occurring  at  the  points  where  the 
rakers  place  their  feet.  It  is  insufficient  that  the  actual  surface 
of  the  loose  hot  mixture  should  represent  a  uniform  thickness;  it 
must  also  be  of  uniform  consistency  all  the  way  through. 

The  lack  of  perfect  form  in  asphalt  surfaces  is  oftener  due 
to  this  cause  than  any  other,  but  it  is,  of  course,  much  empha- 
sized on  streets  of  heavy  travel  where  traffic  depresses  that  part 


418  THE    MODERN    ASPHALT    PAVEMENT. 

containing  the  least  material.  With  coarse  mixtures,  and  those 
deficient  in  filler,  which  do  not  become  so  much  compressed  in 
the  trucks,  and  with  mixtures  poor  in  bitumen,  results  such  as 
have  been  described  are  not  so  apt  to  occur  or  are  brought  out 
less  under  lighter  traffic,  and,  as  a  matter  of  fact,  with  such  mix- 
tures it  is  possible  to  give  a  street  surface  a  much  prettier  original 
finish  than  can  often  be  obtained  with  standard  mixture  which 
carries  a  high  percentage  of  fine  sand,  filler  and  bitumen. 

The  raking  of  the  material  to  a  proper  grade  requires  a  good 
eye  on  the  part  of  the  workman  and  proper  supervision  and  a  bet- 
ter eye  for  such  work  on  the  part  of  the  foreman.  Constant  atten- 
tion and  great  care  are,  however,  the  great  desiderata.  It  is 
not  difficult  to  make  a  good  raker  out  of  an  inexperienced  man 
if  he  is  under  good  supervision.  The  great  difficulty  with  all 
rakers  is  to  make  them  pull  out  all  their  material  to  a  loose  con- 
dition, especially  with  a  dense  mixture  such  as  it  is  necessary  to 
lay  on  heavily  travelled  streets. 

The  hot  mixture  having  been  raked  to  grade,  it  was  the  cus- 
tom, in  the  early  days  of  the  industry  when  the  mixture  was  more 
loose  and  open  and  carried  less  filler  and  asphalt  cement  and 
consequently  had  less  density,  to  give  it  its  first  compression  with 
a  hand-roller  of  comparatively  light  weight.  This  may  be  advis- 
able even  to-day  with  similar  mixtures.  As  a  rule,  however, 
the  modern  mixture  has  sufficient  density  to  permit  the  use  of  a 
steam-roller  at  once,  and  this  is  the  general  custom  in  good  prac- 
tice. The  hot  mixture  is,  however,  allowed  to  cool  to  a  point 
where  it  will  not  be  displaced  or  picked  up.  To  avoid  the  latter 
difficulty  it  may  be  necessary  with  some  mixtures  to  oil  the  roller 
with  a  mixture  of  kerosene  and  water,  and  it  is  generally  found 
to  be  preferable  to  run  the  lighter  or  guide  rolls  of  the  roller  on 
the  surface  first.  After  the  preliminary  compression  the  surface 
is  sprinkled  with  any  fine  mineral  matter  which  will  give  it  a 
color  pleasing  to  the  eye.  It  is  not  necessary  that  this  should 
be  a  hydraulic  cement.  The  excess  of  dust  having  been  swept  off, 
the  surface  is  allowed  to  cool  still  further  until  the  roller  can  go 
on  and  shape  it  up  without  displacing  it.  Experience  can  alone 
determine  what  length  of  time  to  allow  for  cooling.  In  winter 


THE    STREET.  419 

it  cannot  be  long,  since  if  a  hardened  crust  is  allowed  to  form  by 
the  chilling  of  that  portion  of  the  mixture  exposed  to  the  air,  this 
will  have  a  tendency  to  break  up  on  further  rolling,  and  fail  to 
make  a  bond  with  the  main  mass,  resulting  in  subsequent  scaling. 

The  aspect  of  the  finished  pavement,  especially  after  it  has 
been  subjected  to  traffic  for  a  year  or  two,  will  depend  as  much 
on  the  way  it  was  rolled  as  on  the  way  the  mixture  has  been  raked 
out.  The  management  of  a  steam-roller  requires  experience, 
skill,  and  judgment.  The  roller  if  not  run  with  great  regularity 
and  stopped  with  care  at  the  end  of  a  run  will  readily  displace 
the  surface  so  that  it  cannot  be  easily  brought  back  into  form 
again.  The  first  rolling  should  be  with  the  length  of  the  street. 
It  should  then  be  rolled  diagonally  where  this  is  possible  as  soon 
as  it  is  evident  to  the  roller  engineer  that  nothing  is  being  accom- 
plished in  the  original  direction.  No  rule  can  be  laid  down  as 
to  the  length  of  time  necessary  for  rolling  a  given  area  of  surface. 
The  time  will  depend  very  much  on  the  season  of  the  year  and 
more  on  the  character  of  the  mixture.  The  hot  surface  mixture 
will  cool  more  rapidly  in  the  autumn,  and  cannot  be  rolled  for 
the  same  length  of  time  as  in  summer,  or  at  least  with  any  effect. 
Mushy  mixtures,  where  the  local  sands  make  mixtures  of  this 
description,  should  not  be  rolled  too  much.  This  would  injure 
them  by  breaking  the  bond  in  the  cool  mixture.  Mixtures  on  a 
weak  base  cannot  be  rolled  to  the  same  extent  as  those  on  one 
that  is  firm.  Certain  mixtures  which  are  readily  displaced  may 
require  a  final  shaping  up  with  a  roller  of  wider  tread  than  that 
used  for  the  original  compression,  one  of  ten  or  eleven  tons  weight 
and  tread.  This  is  by  no  means  always  necessary  if  the  roller 
engineer  is  skilful  and  the  mixture  a  good  one;  although  the  weight 
per  inch  tread  is  greater  hi  one  case  than  in  the  other.  Follow- 
ing are  some  determinations  of  the  pressure  per  inch  run  for 
various  rollers.  See  table  on  page  420. 

All  rollers  are  not  equally  suited  for  the  work.  Some  are 
strikingly  defective  in  that  they  are  not  well  balanced.  The 
side  carrying  the  motive  power  is  much  heavier  than  the  other, 
and  the  result  is  that  the  roller  sways,  especially  when  it  meets 
an  elevation  or  depression,  thus  producing  a  wavy  surface.  The 


420 


THE    MODERN    ASPHALT    PAVEMENT. 
ROLLERS— PRESSURE  PER  INCH  RUN. 

IROQUOIS    IRON    WORKS. 


Size  of  roller  

2\  tons 

5  tons 

8  tons 

13  tons 

Duplex  engine        . 

4X5 

6X6 

7X7 

8X10 

Main  roll,  width  of  tire.  .... 
Pressure  per  linear  inch  

30  ins. 
125  Ibs. 

38  ins. 
210  Ibs. 

48  ins. 
250  Ibs. 

60  ins. 
300  Ibs. 

best  type  of  modern  roller  has  a  compensating  weight  attached 
to  the  channel  iron  on  the  side  opposite  to  that  carrying  the  motive 
power.  Whether  a  roller  is  properly  balanced  or  not  can  be  deter- 
mined by  running  it  on  a  scantling  so  that  the  latter  is  exactly 
in  the  middle  of  the  rolls  and  then  noting  whether  it  has  a  ten- 
dency to  tip  toward  the  side  carrying  the  motive  power.  If 
it  does  it  should  be  balanced  by  bolting  a  weight  to  the  channel 
iron  on  the  side  which  is  too  light. 

Rollers  should  be  provided  with  a  steering-gear  which  can 
be  controlled  by  power,  thus  enabling  the  engineer  to  give  his 
undivided  attention  to  the  street.  Such  rollers  are  available. 
Throttle-valves  should  be  of  a  kind  which  permit  the  gradual 
reduction  of  speed. 

The  importance  of  having  a  perfect  roller,  if  good  work  is  to 
be  done,  should  not  be  overlooked.  That  offered  by  the  Iroquois 
Iron  Works,  Buffalo,  N.  Y.,  is  the  best  balanced  and  most  care- 
fully constructed  roller  with  which  the  author  is  acquainted.  It 
is  illustrated  in  Fig.  23. 

These  rollers  are  made  of  various  sizes,  2J,  5,  8,  and  13  tons, 
the  latter  being  used  for  rolling  the  base  and  for  finally  shaping 
the  asphalt  surface  where  mixture  requires  it  after  previous  com- 
pression with  a  lighter  roller.  Such  shaping  is  only  necessary 
when  the  mixture  is  of  a  mushy  nature  and  consequently  some- 
what displaced  by  the  roller  of  narrower  tread. 

Work  Under  Particular  Condition. — In  the  preceding  para- 
graphs consideration  has  been  given  only  to  what  may  be  called 
straight  work;  that  is  to  say,  the  laying  of  an  extended  area  where 
everything  connected  with  the  work  goes  on  in  a  perfectly  nor- 
mal way.  This,  however,  is  not  the  only  kind  that  is  met.  There 


422  THE    MODERN    ASPHALT    PAVEMENT. 

are  joints  to  be  made,  between  the  work  of  different  days,  with 
the  curb  and  with  headers,  around  boxes,  manholes,  and  similar 
protuberances,  and  with  railway  tracks  or  the  brick  or  stone 
stretchers  along  them.  It  is  also  quite  possible,  owing  to  unavoid- 
able circumstances,  that  the  surface  may  be  found  to  be,  after 
its  preliminary  compression,  too  high  at  one  point — in  the  gutter 
for  example — or  too  low  at  another.  Owing  to  chilling  of  the 
surface  it  may  not  close  up  properly  or  from  inaccessibility  to 
the  roller  fail  to  be  sufficiently  compressed.  These  conditions 
must  be  met  and  the  defects  remedied,  all  in  their  own  way,  and 
in  many  cases  tools  especially  provided  for  the  purpose,  known 
as  tampers  and  smoothers,  must  be  used.  These  tools  are  shown 
with  some  others  in  the  accompanying  illustration,  from  the  cata- 
logue of  the  Iroquois  Iron  Works  of  Buffalo,  N.  Y.  Fig.  24. 

The  tampers  and  smoothers  must  be  used  with  great  care  and 
should  not  be  too  hot.  If  the  smoothers  are  hot  and  it  is  difficult 
to  tell  their  temperature  in  bright  sunshine,  they  may  do  much 
damage  by  hardening  the  bitumen  in  the  surface,  and  their  use 
is  only  advisable  in  very  skilful  hands.  They  are  a  relic  of  the 
days  when  mixtures  were  used  which  would  not  close  up  readily 
on  account  of  poor  grading  and  deficiency  in  bitumen.  With 
standard  mixture  they  are  seldom  necessary  except  on  joints. 
The  tampers  are  not  as  dangerous,  since  they  are  not  left  in 
contact  with  the  surface  as  long  as  the  smoothers.  They  are 
used  on  joints,  around  manholes,  and  along  rails  at  points 
which  the  roller  cannot  reach  and  in  reducing  inequalities  in  the 
gutter. 

Attempts  to  reduce  projections  above  the  proper  grade  with 
tampers  are  rarely  successful ;  the  material  at  the  point  is  merely 
more  strongly  compressed  than  that  in  the  immediate  neighbor- 
hood, with  the  result  that  the  latter  goes  down  under  traffic  and 
the  original  elevation  is  brought  out  again.  Especially  in  gutters, 
where  the  surface  is  too  high,  the  excess  should  be  removed  with 
a  hot  shovel,  if  necessary,  after  heating  it  with  a  smoothing  iron. 
Except  on  joints  between  days'  work,  the  use  of  tampers  and 
smoothers  is  a  makeshift  to  cover  up  poor  raking,  and  the  best  street 
foreman  will  be  the  man  who  finds  the  least  necessity  for  their 


424  THE    MODERN    ASPHALT    PAVEMENT. 

use,  especially  that  of  the  smoothers,  for  reasons  which  have  been 
already  mentioned. 

Joints  between  different  days'  work,  according  to  the  prefer- 
ence of  the  street  foreman,  are  made  in  different  ways.  Usually 
the  mixture  is  compressed  to  a  feather-edge  under  the  steam- 
roller and  left  in  this  condition.  On  the  following  morning  the 
feather-edge  is  cut  back  to  a  point  where  the  full  thickness  of 
surface  is  shown.  This  edge  is  painted  with  melted  asphalt  and 
the  joint  between  the  two  days'  work  is  made  in  this  way. 

In  the  middle  West  an  excellent  joint  is  made  by  imbedding 
in  the  soft  material,  while  still  hot  and  after  it  has  been  raked 
off  to  a  feather-edge,  a  rope  of  about  f  of  an  inch  in  diameter 
to  which  a  flap  of  canvas  is  attached.  The  steam-roller  is  run 
over  this  until  final  compression  is  obtained,  and  on  the  following 
day  the  rope  and  canvas  are  easily  detached,  leaving  an  excellent 
section  to  work  to  without  the  necessity  of  cutting  back  and 
losing  good  material.  This  form  of  joint  is  to  be  recommended. 

SUMMARY. 

The  preceding  chapter  describes  the  method  of  transporting 
and  handling  on  the  street  the  surface  mixture,  together  with 
the  use  of  the  tools  employed  in  laying  it. 


PART  VI. 

THE    PHYSICAL    PROPERTIES   OF  ASPHALT   SUR- 
FACES. 


CHAPTER  XXI. 

RADIATION,  EXPANSION,  CONTRACTION,  AND  RESISTANCE  TO 

IMPACT. 

THE  physical  properties  of  asphalt  pavements  are  of  interest 
in  two  ways:  first,  from  a  general  point  of  view  as  pertaining  to 
asphalt  surfaces  as  a  whole,  and,  second,  the  peculiar  character- 
istics which  are  dependent  on  particular  mixtures  according  as 
they  differ  in  sand  grading,  the  amount  and  character  of  filler 
they  contain,  and  the  consistency  and  character  of  the  cementing 
material  with  which  they  are  bonded. 

Radiation  from  Asphalt  Pavements. — Asphalt  pavements  have 
been  frequently  criticised  because  of  their  great  absorption  of  heat 
when  exposed  to  summer  suns  in  an  atmosphere  of  high  tem- 
perature and  its  radiation  again  during  the  ensuing  night.  With  a 
view  of  determining  the  number  of  thermal  units  of  heat  thus 
absorbed  and  radiated  numerous  inquiries  have  been  addressed 
to  the  author  as  to  the  specific  heat  of  asphalt.  It  has  been 
assumed  that  the  specific  heat  of  asphalt  could  not  be  very  differ- 
ent from  that  of  other  native  bitumens  the  records  of  which  are 
available.  For  example,  the  specific  heat  of  petroleum  is  given 
by  Pagliani1  as  .498  to  .511.  It  must  be  remembered,  how- 

1  Atti  di  Torino,  1881,  17,  97. 

425 


426  THE   MODERN    ASPHALT    PAVEMENT. 

ever,  that  but  10  to  11  per  cent  of  an  asphalt  surface  consists  of 
bitumen;  the  remainder  is  quartz  and  mineral  matter  which  has  a 
specific  heat  no  greater  than  .201.  The  specific  heat  of  an  asphalt- 
surface  mixture  cannot,  therefore,  be  much  greater  than  that  of  a 
granite  pavement,  or  be  the  cause  of  any  great  difference  in  its 
temperature.  That  the  asphalt  pavement  seems  hotter  must  be 
due  to  other  causes,  and  this  is  to  be  attributed  to  the  fact  that 
having  a  blacker  surface  it  absorbs  heat  rather  more  rapidly  than 
the  granite  and  radiates  it  much  more  rapidly  after  sunset.  There 
is,  therefore,  not  much  more  heat  given  out  by  asphalt  than  by 
granite  pavement,  but  since  it  may  be  given  out  more  rapidly 
it  may  be  more  noticeable.  Each  form  will  give  up  about  the 
same  quantity  during  the  entire  night. 

That  the  figures  assumed  for  the  specific  heat  of  asphalt  are 
not  far  out  of  the  way  may  be  seen  from  the  following  informa- 
tion furnished  in  "  Municipal  Engineering  "  1  by  Mr.  A.  W.  Dow. 


SPECIFIC    HEAT. 

Refined  Trinidad  asphalt 350 

Cuban       asphalt  cement 401 

Trinidad        "  "      381 

Bermudez      "  "      413 

Maracaibo     "  "      447 

Quartz  sand 201 

Maracaibo  and  Bermudez  asphalts,  being  nearly  pure  bitu- 
men, afford  the  best  idea  of  the  true  specific  heat  of  asphalt. 
This  factor  is  somewhat  smaller  than  that  for  petroleum  oil,  and 
this  is  evidently  due  to  the  presence  of  more  condensed  molecules 
in  the  asphalt  than  in  the  oil.2 

Some  experiments  conducted  in  the  summer  of  1907  with 
cylinders  of  granite,  brick  and  asphalt  surfaces,  confirmed  the 
previous  conclusions,  as  will  be  seen  from  the  following  data : 

1  1904,  July,  27,  22. 

'Additional  data  in  regard  to  the  specific  heat  of  mineral  oils  will 
also  be  found  in  "Petroleum,"  Berlin,  2,  521,  April  3,  1907. 


RADIATION,  EXPANSION,  ETC. 


427 


ABSORPTION  AND  RADIATION  OF  HEAT  BY  VARIOUS 
PAVEMENTS. 

MAY,  1907. 


Time. 

Granite. 

Brick. 

Asphalt. 

Thermom. 
Temp. 

Gain  or 
Lose. 

Thermom. 
Temp. 

Gain  or 
Loss. 

Thermom. 
Temp. 

Gain  or 
Loss. 

10.30 
11.30 
12.30 
3.00 
4.00 

72.0 
93.2 
102.2 
98.6 
84.2 

+    21.2 
-f   30.2 
-     4.6 
-  18.0 

73.4 
93.2 
101.3 
101.3 
86.0 

72.0 
91.4 
100.4 
100.4 
86.0 

+  19.8 
+  27.9 
+  27.9 
-  15.3 

+  19.4 

+  28.4 
+  28.4 
-  14.4 

JUNE,  1907. 


11.05 

80.6 

80.6 

78.8 

11.35 
12.05 
2.35 
3.05 
4.05 

88.0 
91.5 
92.8 
87.8 
84.2 

-f    7.4 
+  10.9 
-f  12.2 
5.0 
-    8.6 

90.6 
93.2 
93.6 
89.4 
84.2 

-1-  10.0 
-f  12.6 
-1-  13.0 
-    4.2 
-    9.4 

89.6 
92.0 
91.4 

87.8 
84.2 

+  10.8 
+  13.2 
+  12.6 
-    3.6 
-    7.2 

JUNE,  1907. 


11.15 

81  5 

83.4 

82.4 

11.45 

89.6 

+    8.1 

93.1 

+    9.7 

93.1 

+  10.7 

12.05 

93.0 

+  11.5 

96.8 

+  13.4 

96.8 

+  14.4 

2.05 

103.8 

+  22.3 

105.8 

+  22.4 

105.8 

+  23.4 

3.15 

93.0 

-  10.8 

93.2 

-  12.6 

91.4 

-14.4 

4.30 

86.0 

-  17.8 

85.2 

-  20.6 

84.2 

-  21.6 

Black  bulb  thermometer  in  each  case  90°  F.  to  98°  F.  in  sun. 
Air  temperature,  May,  73°  F.  to  84°  F. 

June,  81°  F.  to  92°  F.  and  81°  F.  to  93°  F. 
Clearer  atmosphere  on  second  day. 

Expansion  and  Contraction  of  an  Asphalt  Surface. — Asphalt 
surfaces  necessarily  expand  and  contract  with  changes  of  tem- 
perature. As  they  consist  very  largely,  to  the  extent  of  about 
89  per  cent,  of  mineral  matter,  this  expansion  must  be  closely 
that  of  quartz,  of  which  the  mineral  aggregate  is  principally  com- 
posed and  must  be  fairly  constant  for  all  surfaces.  Whether  the 
cementing  material  is  sufficiently  strong  to  yield  to  such  con- 


428  THE  MODERN  ASPHALT  PAVEMENT. 

traction  without  the  fracture  will  determine  whether  the  pave- 
ment cracks  or  not.  It  is,  of  course,  a  feature  which  will  vary 
with  the  character  of  every  mixture,  depending  upon  its  com- 
position. This  subject  will  be  taken  up  in  detail  in  a  succeeding 
chapter,  where  the  cause  of  cracks  in  pavements  is  considered.1 

Impact  Tests  of  Asphalt-surface  Mixture. — The  force  which 
has  the  greatest  tendency  to  injure  an  asphalt  surface  is  that  of 
impact.  The  blows  from  horses'  hoofs  or  from  the  wheels  of 
vehicles  where  the  surface  is  irregular  deteriorates  it  to  a  much 
larger  extent  than  attrition  or  ordinary  travel.  A  well-con- 
structed asphalt  surface  has  been  known  to  carry  without  injury 
a  load  of  51  tons  on  a  truck  with  broad  tires,  whereas  the  same 
pavement  under  constant  impact  would  deteriorate  perceptibly 
in  the  course  of  years. 

The  capacity  of  any  asphalt  surface  to  resist  impact  can  be 
readily  tested  in  the  laboratory  with  appropriate  testing 
machines,  such  as  that  devised  by  Mr.  Logan  Waller  Page, 
of  the  Office  of  Public  Roads,  and  described  on  page  34 
of  Bulletin  No.  79  of  the  Bureau  of  Chemistry,  and  which 
is  illustrated  in  Fig.  25.  Cylindrical  test-pieces  are  made 
from  the  surface  mixture  to  be  examined  in  a  mold  which  permits 
of  its  being  filled  with  the  hot  mixture  at  an  appropriate  tem- 
perature and  of  being  compressed  by  means  of  blows  with  a  ham- 
mer of  four  pounds  weight,  ten  of  which  are  given  to  each  end 
of  the  cylinder.  These  cylinders  are  usually  made  1.25  inches 
in  diameter  and  1  inch  high,  and  weigh  about  50  grams.  When 
brought  under  the  impact  machine  they  are  held  firmly  with  a 
plunger  resting  on  the  surface  with  a  spherical  bearing  having  a 
radius  of  4/10  of  an  inch.  The  hammer  is  then  allowed  to  drop 
from  a  distance  of  1  cm.,  and  this  distance  is  increased  by  this 
amount  at  each  blow  until  the  test-piece  yields.  Under  these 
conditions  tests  have  shown  that  the  resistance  of  any  asphalt 
surface  to  impact  will  depend  upon: 

1.  The  sand  grading. 

2.  The  character  of  the  sand. 

1  See  page  480. 


RADIATION,  EXPANSION,  ETC 


429 


c 


FIG.  25. — Instrument  for  Impact  Test. 


430 


THE  MODERN  ASPHALT  PAVEMENT. 


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RADIATION,  EXPANSION,  ETC. 


431 


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432 


THE  MODERN  ASPHALT  PAVEMENT. 


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RADIATION,  EXPANSION,  ETC. 


433 


3.  The  amount  of  filler  present. 

4.  The  character  of  the  asphalt  in  use. 

5.  The  consistency  of  the  asphalt. 

6.  The  density  and  degree  of  compaction  of  the    test-piece. 

7.  The  percentage  of  bitumen  in  the  mixture. 

The  data  in  the  preceding  tables  will  illustrate  the  application 
of  the  test. 

From  these  results  it  appears  that  the  old-time  mixtures  which 
are  low  in  bitumen,  those  from  Minneapolis  and  Rochester,  do  not 
withstand  impact  to  nearly  the  extent  that  the  more  modern 
mixtures  do,  and  reveal  the  cause  of  the  inferiority  of  the  pave- 
ments constructed  with  such  mixtures. 

The  results  of  tests  by  impact  at  different  temperatures  of 
the  standard  New  York  mixture  made  with  various  asphalts 
show  that  those  in  which  Trinidad  lake  asphalt  is  the  cementing 
material  give  a  much  greater  resistance  to  impact  at  low  and 
medium  temperatures,  and  are  much  less  affected  by  tempera- 
ture changes  than  those  made  with  Bermudez  asphalt,  while  the 
variation  in  the  character  and  grading  of  the  sand,  and  the  per- 
centage of  filler  and  of  bitumen,  are  made  evident  by  other  data 
in  the  table. 

It  should  also  be  observed  that  the  work  done  in  fracturing 
the  test-pieces  is  relatively  as  the  square  of  the  number  of  blows. 

The  impact  test  is  also  valuable  in  revealing  the  difference  in 
susceptibility  to  water  action  of  different  mixtures.  Cylinders 
of  standard  Trinidad  and  Bermudez  asphalt  mixtures  were  pre- 
pared and  some  of  them  tested  by  impact  at  78°  Fahr.  as  soon  as 
made.  Others  were  immersed  hi  water  for  three  months  and  the 


Trinidad. 

Bermudez. 

Density  

2.24 

2.24 

Number  of  blows: 
Original  material 

21 

16 

After  three  months'  exposure 
to  running  water  

20 

13 

Water  absorbed: 
Pounds  per  square  yard 

129 

157 

434  THE    MODERN    ASPHALT   PAVEMENT. 

amount  absorbed  determined,  after  which  they  were  subjected  to 
the  impact  test.  The  results  are  shown  in  the  table  at  bottom  of 
page  433. 

It  is  readily  seen  that  the  Bermudez  mixture  is  much  more 
weakened  by  immersion  in  water  than  that  made  of  Trinidad 
asphalt.  The  value  of  the  impact  test  is,  therefore,  assured  from 
the  results  thus  far  obtained  and  the  investigation  of  the  subject 
will  be  carried  out  in  greater  detail  in  the  future. 

SUMMARY. 

In  the  preceding  pages  the  question  of  the  radiation  of  heat 
from  asphalt  pavements,  their  expansion  and  contraction,  and 
resistance  of  various  asphalt  surface  mixtures  to  impact  are 
considered. 


PART  VII. 

SPECIFICATIONS  FOR  AND  MERITS  OF  ASPHALT 
PAVEMENTS. 


CHAPTER  XXII. 
SPECIFICATIONS. 

As  has  already  been  mentioned,  the  specifications  for  the  con- 
struction of  asphalt  pavements  which  are  prepared  by  engineers 
who  are  not  thoroughly  acquainted  with  the  subject  are  often 
wanting  in  some  respects  or  make  certain  requirements  which 
are  undesirable,  unessential,  or  unnecessarily  increase  the  cost  of 
the  pavement.  For  the  construction  of  an  asphalt  pavement 
which  is  to  meet  the  requirements  of  ordinary  traffic  in  a  majority 
of  our  cities  the  following,  in  the  author's  opinion,  will  be  found 
to  be  a  thorough  protection  of  the  city's  interests,  and  not  open 
to  objection  by  the  bidders  that  the  provisions  are  unreasonable. 

SPECIFICATIONS  FOR  ASPHALT  PAVEMENT  ON  PORTLAND-CEMENT 
CONCRETE  FOUNDATION.1 

Extent  of  Work. — The  work  shall  consist  of  regulating  and 
grading  the  entire  street,  constructing  combined  curb  and  gutter, 
laying  asphalt  pavement,  and  all  work  incidental  thereto,  all  in 
accordance  with  the  following  specifications: 

Removal  of  Old  Materials. — All  old  material  which  is  not  to 
be  used  in  the  work,  shall  become  the  property  of  the  contractor 
and  be  removed  by  him. 

1  As  an  example  of  the  type  of  specifications  in  actual  use  in  cities,  those 
portions  pf  the  specifications  of  Kansas  City,  Mo.,  which  apply  to  the  tech- 
nical portion  of  the  work  are  presented  in  an  appendix. 

435 


436  THE   MODERN  ASPHALT  PAVEMENT. 


GRADING. 

Excavation,  Grading  and  Preparation  of  Foundation. — Any 

old  material  to  be  used  again  shall  be  compactly  piled  on  the  side 
of  the  roadway.  The  excavation  shall  be  carried  to  the  grade 
established  by  the  Engineer.  When  completed,  the  sub-grade 
shall  present  a  line  and  contour  parallel  with  and  approximately 
„ . .  .inches  below  the  surface  of  the  finished  pavement  to  be  con- 
structed. Should  any  soft,  spongy,  vegetable  or  other  objection- 
able matter  be  disclosed  by  the  excavation  thus  made,  or  be 
located  where  filling  is  to  be  done,  such  material  shall  be  removed 
and  replaced  with  suitable  material,  which  shall  be  thoroughly 
compacted.  Whenever  deemed  necessary  by  the  Engineer,  the 
sub-grade  shall  be  rolled  with  a  suitable  steam  roller. 

Inspection  and  Piling  of  Material. — The  materials  for  con- 
struction, when  brought  upon  the  street,  shall  be  neatly  piled 
so  as  to  present  as  little  obstruction  as  possible  to  travel.  No 
material  shall  be  used  without  the  approval  of  the  Engineer,  the 
contractor  furnishing  all  labor  necessary  for  inspection,  without 
&ny  charge. 

Filling  .and  Embankments. — Embankments  shall  be  brought 
up  to  the  designated  grades,  and  the  top  shaped  off  and  compacted 
as  defined  for  earth  excavation.  Such  excavated  material  as 
may  be  fit  for  the  purpose  and  as  may  be  necessary,  shall  be  used 
U>  fill  in  those  parts  of  the  streets  which  are  below  the  aforesaid 
grades. 

CONCRETE. 

Upon  the  sub-grade,  prepared  as  above  described,  Portland- 
cement  concrete  composed  of  Portland  cement,  clean  sharp  sand, 
and  broken  stone  or  slag,  will  be  laid  to  an  average  thickness  of 

inches.      Suitable  gravel  may  be  used  in  combination  with 

the  stone  or  slag,  as  hereinafter  provided.  The  cement  shall  be 
of  the  best  quality  of  American  manufacture  and  shall  be  sub- 
mitted to  the  Engineer  for  "inspection  at  least  ten  (10)  days  before 
it  is  used.  It  shall  conform  to  the  following  tests,  conducted 


SPECIFICATIONS.  437 

according  to  the  methods  recommended  by  the  Committee  on 
Uniform  Tests  of  Cement  of  the  Am.  Soc.  of  C.  E.  It  shall  not 
set  in  less  than  one  (1)  hour.  When  mixed  in  the  proportion  of 
one  (1)  part  of  cement,  by  weight,  and  three  (3)  parts  of  standard 
sand,  it  shall  have  a  tensile  strength  after  exposure  of  one  (1) 
day  in  air  and  six  (6)  days  in  water  of  at  least  one  hundred  and 
fifty  (150)  pounds. 

The  sand  shall  be  clean  and  sharp,  not  more  than  20  per  cent 
of  which  shall  pass  a  50-mesh  screen.  It  shall  be  free  from  loam 
adherent  to  the  sand  grains.  The  gravel  shall  be  of  such  size 
that  it  will  satisfactorily  fill  the  voids  in  the  broken  stone,  and 
it  shall  not  contain  dirt  or  foreign  matter.  The  broken  stone 
shall  consist  of  granite,  trap,  or  other  hard  rock  or  slag  which  shall 
be  satisfactory  to  the  Engineer.  It  shall  be  of  such  a  size  that 
all  will  pass  through  a  revolving  screen,  having  holes  two  and  one- 
half  (2^)  inches  in  diameter,  and  be  retained  by  a  screen  having 
holes  one-half  (£)  inch  in  diameter.  Stone  which  is  the  run  of  the 
crusher  may  be  used  when  provision  is  made  for  the  consideration 
of  finer  particles  than  one-half  (^)  inch  which  it  contains  as  sand. 
The  unit  of  measure  in  mixing  these  materials  will  be  the  barrel 
of  cement,  weighing  380  pounds,  and  four  (4)  cubic  feet  for  sand, 
gravel,  and  stone.  They  shall  be  mixed  in  the  following  propor- 
tions and  in  the  following  manner: 

The  sand  and  cement  shall  be  mixed  dry  in  the  proportion  by 
volume  of  one  (1)  of  cement  to  three  (3)  of  sand,  and  then  made 
into  a  mortar  by  the  addition  of  water.  To  this  mortar  will 
be  added  six  (6)  measures  of  wet  broken  stone,  and  the  whole 
thoroughly  mixed  by  hand  or  machinery  until  it  is  entirely  uni- 
form. 

Where  gravel  is  available  this  may  be  used  in  such  proportion 
that  the  gravel  will  fill  the  voids  in  the  broken  stone,  with  a  con- 
sequent decrease  in  the  amount  of  mortar  necessary  to  make  a 
compact  concrete.  For  example:  A  one  (1)  to  three  (3)  mortar 
which  could  be  mixed  with  only  six  (6)  parts  of  broken  stone 
may  be  mixed  with  a  combination  of  two  (2)  to  three  (3)  parts 
of  gravel  and  four  (4)  to  six  (6)  parts  of  broken  stone.  The  con- 
crete thus  mixed  will  be  of  such  a  consistency,  owing  to  the  per- 


438  THE    MODERN    ASPHALT    PAVEMENT. 

centage  of  water  which  it  contains,  that  it  shall  quake  very  slightly 
when  thoroughly  rammed. 

The  concrete  as  thus  prepared  shall  then  be  spread  on  the 
sub-grade  and  rammed,  the  surface  being  so  graded  that  in  its 
finished  condition  it  shall  average ....  inches  below  that  of  the 
finished  pavement.  No  concrete  shall  be  used  that  has  been 
mixed  more  than  one  hour. 

The  concrete,  after  laying,  shall  be  properly  protected  and 
the  surface  shall  be  kept  moist  in  warm  weather  by  sprinkling 
at  proper  intervals. 

At  the  expiration  of  such  a  period  as  is  found  to  be  necessary 
in  order  that  the  concrete  shall  have  attained  a  sufficient  set  to 
sustain  a  steam  roller,  the  binder  course  shall  be  laid. 

ASPHALT  PAVEMENT. 

Definition. — The  pavement  proper  shall  consist  of  a  binder 
'course ....  inches  in  thickness  and  a  wearing  surface. ..  .inches 
in  thickness,  equal  in  composition  to  the  pavement  mixture  here- 
inafter described. 

BINDER  COURSE. 

The  alternative  of  an  open  or  close  binder  course  is  given. 
In  any  specification  but  one  should  be  called  for.  The  close 
binder  course  is  much  more  desirable. 

Open  Binder. — Stone. — The  binder  shall  be  composed  of 
suitable  clean  broken  stone  passing  a  one  and  a  quarter  (1J) 
inch  screen. 

Asphaltic  Cement. — The  stone  shall  be  heated  in  suitable 
appliances,  not  higher  than  300°  Fahrenheit,  and  then  thoroughly 
mixed  by  machinery  with  asphaltic  cement  equivalent  in  com- 
position to  that  hereinafter  set  forth,  in  such  proportion  as  will 
cover  the  stone  with  a  glossy  coat  and  without  any  excess  of 
asphaltic  cement. 

Laying. — The  binder  must  be  hauled  to  the  work  and  spread 
while  hot  upon  the  foundation  to  such  thickness  that,  after 
being  immediately  compacted  by  rolling,  its  average  depth 
shall  be ....  inches,  and  its  upper  surface  shall  be  approximately 


SPECIFICATIONS.  439 

parallel  to  the  surface  of  the  pavement  to  be  laid.  Upon  this 
binder  course  shall  be  laid  the  wearing  surface. 

No  traffic,  except  such  as  may  be  required  in  depositing  the 
surface  mixture  or  in  otherwise  prosecuting  the  work,  shall  be 
allowed  on  the  binder  course. 

Compact  or  Close  Binder. — Compact  or  close  binder  shall 
be  composed  of  hard,  clean  broken  stone  which  shall  pass  an 
opening  one  (1)  inch  in  diameter,  the  voids  in  which  are  filled 
with  finer  stone  passing  an  opening  three-eights  (|)  inch  in  diameter, 
while  the  voids  in  the  mixed  stone  shall  be  filled  with  a  well 
graded  sand  or  old  asphalt  surface  mixture  which  has  previously 
been  in  use,  and  which  has  been  softened  by  heating  so  as  to  allow 
it  to  be  incorporated  properly  with  the  stone.  If  sand  is  used, 
sufficient  asphalt  cement  shall  be  added  to  thoroughly  coat  the 
mineral  aggregate  with  bitumen  without  showing  any  excess  on 
compression  with  a  hot  tamper,  while  if  old  surface  material  is 
used,  sufficient  cement  shall  be  used  to  coat  the  stone  and  produce 
the  same  result. 

Care  should  be  exercised  with  close  binder  that  it  does  not 
carry  an  excess  of  fine  material  or  of  asphalt  cement,  as  in  this 
case  the  wearing  surface  of  the  pavement  may  have  a  tendency 
to  displacement. 

Asphaltic  Cement. — The  asphaltic  cement  for  the  binder 
course  should  have  a  consistency  of  at  least  twenty  (20)  points, 
as  indicated  by  the  Bowen  machine,  higher  than  that  in  use 
in  the  surface. 

Pavement  Mixture. — The  pavement  mixture  for  the  wearing 
surface  shall  be  composed  of: 

(a)  Asphaltic  cement  (Refined  asphalt  and  flux). 

(6)  Sand  of  satisfactory  grading  and  grain. 

(c)  Filler,   consisting  of  finely  powdered  mineral  matter. 

Asphaltic  Cement. — The  asphaltic  cement  shall  be  composed 
of  refined  asphalt  and  flux  of  such  character  that  the  bitumen, 
without  regard  to  the  mineral  matter  present,  shall  be  a  homo- 
geneous solution,  and  present  the  following  characteristics: 

1.  The  proportion  of  bitumen  soluble  in  88-degree  naphtha 


440  THE  MODERN  ASPHALT  PAVEMENT. 

shall  not  exceed  seventy-eight  (78)  per  cent,  nor  fall  below  sixty- 
four  (64)  per  cent. 

2.  A  No.  2  needle,  weighted  with  one  hundred  (100)  grams, 
shall  penetrate,  in  five  (5)  seconds,  at  78°  F.,  a  distance  of  from 
three  (3)  to  nine  (9)  millimeters. 

3.  When  twenty  (20)  grams  are  heated  in  a  receptacle  about 
two  and  a  half  (2£)  inches  in  diameter  and  about  two  (2)  inches 
high,  for  seven  (7)   hours,  in  an  oven  maintained  at  a  uniform 
temperature  of  about  325°  F.,  as  determined  by  a  thermometer, 
the  bulb  of  which  is  immersed  in  a  similar  receptacle  filled  with 
oil,  it  shall  not  lose  more  than  four  (4)  per  cent.     Its  flash  point 
as  determined  in  a  New  York  State  closed  oil  tester,  shall  not 
be  less  than  350°  F. 

4.  Ninety-five  (95)  per  cent  shall  be  soluble  in  carbon  disulphide 
at  air  temperature,  and  not  more  than  one  and  a  half  (1£)  per  cent 
of  the  bitumen  shall  be  less  soluble  in  carbon  tetrachloride  than 
in  carbon  disulphide,  the  test  for  the  former  being  conducted 
by  submitting  the  bitumen  to  the  action  of  the  tetrachloride 
for  twenty-four  (24)  hours  before  filtration. 

Sand. — The  sand  shall  consist  of  hard  grains,  not  necessarily 
sharp,  but  not  containing  more  than  one  (1)  per  cent  of  clay 
or  loam.  On  sifting,  the  entire  amount  shall  pass  a  ten  (10) 
mesh  screen,  at  least  fifteen  (15)  per  cent  shall  pass  an  eighty 
(80)  mesh  screen,  and  seven  (7)  per  cent  a  one-hundred  (100) 
mesh  screen. 

Filler. — 1.  Powdered  Mineral  Matter  or  Dust. — The  filler 
shall  consist  of  ground  limestone  or  any  other  mineral  matter 
of  sufficient  density  to  produce  a  powder  having  a  volume  weight 
of  at  least  ninety  (90)  pounds  to  the  cubic  foot.  It  shall  be  so 
fine  that  at  least  sixty-six  (66)  per  cent  shall  pass  a  two-hundred 
(200)  mesh  screen,  and  all  of  it  shall  pass  a  fifty  (50)  mesh  screen, 
while,  when  thoroughly  agitated  with  distilled  water  at  a  tem- 
perature of  68°  F.,  by  means  of  an  air  blast,  avoiding  cyclonic 
effects,  not  more  than  forty  (40)  per  cent  shall  subside  on  standing 
for  fifteen  (15)  seconds. 

2.  Portland    Cement. — The    filler    shall    consist    of    Portland 


SPECIFICATIONS.  441 

cement  of  such  a  degree  of  fineness  that  seventy-five  (75)  per  cent 
will  pass  a  two-hundred  (200)  mesh  sieve. 

Only  one  or  the  other  of  the  materials  described  as  filler  should 
be  called  for  in  any  specification,  as  the  difference  in  cost  between 
the  two  is  sufficient  to  require  a  separate  estimate  on  each. 

Combining  Materials. — The  materials  complying  with  the 
above  specifications  shall  be  mixed  in  proportions  by  weight, 
depending  upon  their  character.  The  percentage  of  matter  soluble 
in  carbon  disulphide  in  any  pavement  mixture  shall  be  not  less 
than  9.5  nor  more  than  12.0  per  cent. 

The  sand  and  the  asphaltic  cement  will  be  heated  separately 
to  such  temperatures  that  the  finished  mixture  shall,  depending 
on  the  asphalt  in  use,  have  a  temperature  of  from  290°  to 
330°  Fahr.  The  filler  shall  be  mixed,  while  cold,  with  the  hot 
sand.  The  asphaltic  cement  will  then  be  mixed  with  the  sand 
and  stone  dust,  at  the  required  temperature  and  in  the  proper 
proportion  in  a  suitable  apparatus,  so  as  to  effect  a  thoroughly 
homogeneous  mixture. 

Laying  the  Pavement. — The  above  mixture  shall  be  hauled 
to  the  street  in  trucks  properly  protected  from  radiation  by 
tarpaulins  at  a  temperature  of  not  less  than  250°  Fahr.,  and  spread 
upon  the  binder  to  such  a  depth  as  will  insure  an  average  thick- 
ness of inches  after  ultimate  compression.  This  compression 

will  be  attained  by  first  smoothing  the  surface  with  a  hand-roller, 
or  light  steam-roller,  after  which  hydraulic  cement  or  stone  dust 
shall  be  swept  over  it,  when  the  rolling  will  be  continued  with  a 
steam-roller  until  the  surface  is  properly  compacted. 


BITUMINOUS  CONCRETE  PAVEMENT. 

For  a  bituminous  concrete  surface,  the  character  of  the  asphalt 
cement,  sand,  filler  and  stone  will  be  the  same  as  those  provided 
for  in  the  previous  specifications. 

Determination  of  Proportions. — The  wearing  surface  mixture 
shall  be  composed  of  the  materials  previously  specified  combined 
in  proportions  to  be  determined  as  follows: 

The  stone  shall  be  separated  into  fragments  which  are  retained 


442  THE  MODERN  ASPHALT  PAVEMENT. 

and  those  which  pass  a  screen  with  circular  openings  of  three- 
eighths  (|)  inch  size.  While  hot,  a  layer  of  the  coarser  fragments 
are  to  be  spread  on  the  bottom  of  a  strong  box  exactly  one  foot 
square  and  shaken  down.  Hot  fragments  of  the  smaller  size 
are  then  shaken  into  the  voids  in  the  larger  stone  until  the  latter 
are  filled.  Into  this  mixture  hot  sand  and  filler,  in  the  proportion 
of  ninety  (90)  per  cent  sand  and  ten  (10)  per  cent  filler,  are  sifted, 
with  continued  jolting  and  jarring  of  the  box,  until  the  stone  has 
taken  up  all  of  the  fine  material  possible.  This  operation  is 
repeated  with  subsequent  layers  until  the  box  is  full.  It  is  then 
struck  off  evenly  and  weighed.  The  total  weight  of  the  mineral 
matter  in  the  box  obtained  in  this  way  is  divided  by  the  weight 
of  a  solid  cubic  foot  of  mineral  matter  of  the  same  density,  and 
the  voids  in  the  mixture  of  rock,  sand  and  filler  determined.  The 
voids  should  not  exceed  25  per  cent. 

The  proportions  by  weight  in  which  the  different  components 
are  present  is  then  determined  either  by  screening  the  contents 
of  the  box  or  by  originally  taking  a  definite  amount  of  each  and 
determining  by  difference  the  amount  actually  placed  in  the  box. 
These  proportions  shall  be  those  which  shall  be  subsequently  used 
in  making  up  the  mineral  aggregate  for  the  surface  mixture 
unless  observation  on  the  street  in  laying  the  mixture  should 
indicate  the  necessity  for  increasing  the  amount  of  fine  material 
present. 

The  proportions  will  ordinarily  vary  between  the  following 
limits: 

Coarse  stone 56  to  30% 

Fine  stone 16"  26 

Sand 25"  33 

FUler 3"      5 

The  variations  will  depend  upon  the  shape  of  the  fragments 
of  the  coarse  stone  and  on  the  uniformity  in  size  of  the  fragments 
of  the  two  dimensions. 

The  amount  of  bituminous  cement  necessary  to  coat  the 
particles  of  the  above  mineral  aggregate  and  fill  the  voids  therein 
as  nearly  as  possible,  shall  be  determined  as  follows: 


SPECIFICATIONS.  443 

To  the  hot  mineral  aggregate  assembled  in  the  proportions 
arrived  at  as  above,  shall  be  added  the  bituminous  cement  in 
an  amount  which  previous  experience  points  out  as  within  the 
limits  for  such  a  mixture.  After  thorough  mixing  the  material 
prepared  in  this  way  is  placed  upon  a  firm  surface  (such  as  one 
of  hydraulic  concrete)  and  compacted  with  a  hot  tamper  until 
it  is  thoroughly  compressed.  If  bitumen  comes  to  the  surface 
to  a  slight  extent,  the  amount  used  is  satisfactory,  but  if  it  appears 
in  excess,  the  amount  of  bituminous  cement  must  be  diminished, 
or,  if  it  appears  dry,  it  must  be  increased  until  the  proper  appear- 
ance is  obtained.  The  percentage  thus  determined  will  be  followed 
in  making  the  surface  for  the  street,  but  it  may  be  modified  to 
a  certain  extent  to  correspond  to  unavoidable  variations  in  the 
mineral  aggregate,  but  in  no  case  shall  it  exceed  8.0  per  cent, 
nor  fall  below  6.5  per  cent. 

Preparation  and  Mixing  of  Bituminous  Wearing  Surface. — 
The  sand  and  stone  shall  be  heated  in  suitable  heaters  to  the  re- 
quired temperature,  which  temperature  shall  be  dependent  upon 
that  of  the  atmosphere  at  the  time  the  mixing  is  in  progress,  and 
upon  the  character  of  the  bituminous  cement  in  use.  These 
materials,  while  in  this  heated  condition,  shall  be  separated  into 
not  less  than  three  sizes  by  passing  over  a  screen  having  perfora- 
tions or  openings  of  at  least  two  diameters,  so  arranged  as  to 
separate  the  stone  and  sand  into  particles  larger  than  three-eighths 
(I)  inch  in  their  greatest  diameter,  particles  passing  a  screen 
with  openings  three-eighths  (f )  in  size  and  retained  on  a  10-mesh 
screen,  and  particles  passing  the  latter  screen;  the  material  of 
each  size  being  collected  separately  in  suitable  bins.  The  material 
of  each  size  shall  then  be  weighed  or  measured  out  in  the  proportions 
determined  upon,  together  with  a  proper  proportion  of  filler 
(finely  ground  mineral  matter)  not  previously  heated.  The 
aggregate  shall  then  be  mixed  with  the  bituminous  cement,  pre- 
pared as  described  in  the  paragraph  on  this  material  above  given, 
in  a  suitable  mixing  appliance,  either  pans  or  a  double-bladed 
revolving  mixer  of  the  type  generally  used  in  the  preparation  of 
bituminous  paving  mixtures,  the  operation  of  mixing  to  be  con- 
tinued until  uniformity  is  attained. 


444  THE  MODERN  ASPHALT  PAVEMENT. 

Laying  Bituminous  Wearing  Surface. — In  this  condition  the 
bituminous  wearing  surface  mixture  shall  be  hauled  to  the  street 
in  suitable  carts  or  wagons,  properly  protected  from  the  weather, 
so  as  to  prevent  an  undue  loss  in  temperature.  It  shall  be  spread 
upon  the  foundation  with  hot  rakes  to  such  a  depth  that  after 
receiving  its  ultimate  compression  by  rolling  with  a  steam  roller, 
it  will  have  an  average  thickness  of  two  (2)  inches. 

Surface  Finish. — After  the  rolling  of  the  bituminous  wearing 
surface  has  been  completed,  there  shall  be  spread  over  it  a  thin 
coating  of  quick-drying  bituminous  flush-coat  composition, 
specially  prepared,  the  purpose  of  this  coating  being  to  thoroughly 
fill  and  smooth  out  any  unevenness  which  may  be  on  the  surface 
of  the  coarser  mixture. 

There  shall  then  be  spread  over  and  rolled  into  the  wearing 
surface  a  thin  layer  of  coarse  sand  or  stone  chips  for  the  purpose 
of  presenting  a  gritty  surface,  which  shall  not  be  slippery.  The 
character  and  size  of  the  sand  or  stone  chips  to  be  spread  upon  the 
surface,  and  the  consequent  degree  of  roughness  of  surface,  shall 
be  determined  by  the  Engineer,  who  may,  at  his  discretion, 
omit  the  use  of  stone  chips  and  substitute  therefor  a  light  sweep- 
ing of  hydraulic  cement,  stone  dust,  or  similar  material,  in  order 
to  secure  a  smoother  surface. 


MATERIAL  FOR  REPAIRS. 

Repairs. — In  case  of  repairs,  it  shall  be  required  that  such 
repairs  be  made  with  a  pavement  mixture  equal  to  the  above 
described. 

CLEARING  UP. 

All  surplus  materials,  earth,  sand,  rubbish,  and  stones  are  to 
be  removed  from  the  line  of  the  work.     All  material  covering  the* 
pavement  and  sidewalks  shall  be  swept  into  heaps  and  imrne 
diately  removed  from  the  line  of  the  work. 


SPECIFICATIONS.  445 


MAINTENANCE. 

Contractor  to  Make  Repairs. — The  contractor  shall  make  all 
repairs  which  may  be  necessary  during  a  period  of  ....  years l 
from  the  date  of  acceptance  of  the  pavement,  which  are  caused 
by  improper  construction  due  to  defective  materials  or  workman- 
ship, and  he  guarantees  that  he  will  repair  during  this  period, 
any  and  all  defects  arising  through  its  usual  use  as  a  roadway. 
In  case  of  the  contractor's  failure  or  neglect  to  do  so  within  thirty 
days  after  notification  by  the  duly  authorized  official,  such  notice 
to  be  served  upon  him  in  writing,  either  personally  or  by  leaving 
said  notice  at  his  place  of  business  or  with  his  agent  in  charge 
of  the  work,  the  said  duly  authorized  official  may  repair,  or  cause 
such  defects  to  be  repaired,  and  may  recover  cost  thereof  from 
the  contractor  or  his  sureties. 

Temporary  Repairs  in  Winter.  —The  contractor  shall  have 
the  right,  in  case  of  trenches,  to  provide  against  settlement  by 
covering  the  surface  of  the  cut  with  broken  stones  and  maintain- 
ing the  surface  for  a  sufficient  period,  and  during  winter  weather 
any  hole  in  the  pavement  may  be  filled  and  maintained  with 
binder,  asphalt  mastic,  or  other  suitable  material. 

Repairs  to  Openings. — During  the  period  of  maintenance, 
the  contractor  shall,  within  thirty  (30)  days  after  the  receipt 
of  notice  so  to  do,  restore  the  pavement  over  all  openings  made 
under  permits  legally  issued  by  the  duly  authorized  official  for 
new  service  connections,  or  repairing,  renewing,  or  removing 
the  same,  and  over  all  trenches  made  for  carrying  sewers, 
water  or  gas  pipes  or  any  other  sub-surface  pipes  or  conduits, 
for  the  sum  of  $3.50  per  square  yard  for  any  opening  less  than 

1  The  author  has  suggested  no  definite  period  of  guaranty  as  there  is  a 
tendency  on  the  part  of  the  larger  cities  to  shorten  this  to  a  very  "consider- 
able extent,  New  York,  Chicago,  Philadelphia,  and  St.  Louis  now  calling 
for  five  years,  while  in  the  State  of  California  no  guaranty  whatever  is 
required.  Shorter  periods  are  called  for  in  view  of  the  fact  that  municipal 
officials  are  now  in  a  position  to  judge  of  the  character  of  the  work  that  is 
being  done  on  any  contract  before  acceptance,  which  was  not  the  case 
years  ago. 


446  THE    MODERN    ASPHALT  PAVEMENT. 

ten  (10)  square  yards  in  area,  and  $3.00  per  square  yard  over  any 
trench  measuring  more  than  ten  (10)  square  yards  in  area;  $3.25 
per  square  yard  for  restoring  the  pavement  over  any  opening 
between  or  alongside  of  surface  railroad  tracks  which  shall  exceed 
ten  (10)  square  yards  in  area,  and  in  case  of  any  injury  to  the 
surface  of  the  pavement  caused  by  fire  or  accident,  same  shall  be 
replaced  for  the  sum  of  $2.00  per  square  yard.  The  concrete 
foundation,  if  relaid,  shall  be  of  the  same  thickness  as  that  origi- 
nally laid.  The  contractor  will  not  be  held  responsible,  during 
the  period  of  guaranty,  for  any  defects  in  the  pavement  or  mate- 
rials, which  may  have  been  caused  by  the  opening  of  trenches 
or  by  the  improper  backfilling  of  the  same,  and  will  not  be  com- 
pelled to  do  the  repaving  over  said  trenches,  except  as  herein- 
before provided,  nor  shall  he  be  held  responsible  for  deterioration 
of  the  pavement  along  the  rails  of  street  railway  tracks,  if  the 
form  of  construction  is  such  that  the  rail  vibrates  under  the  traffic 
it  carries,  unless  the  track  construction  has  been  in  charge  of  the 
contractor  himself,  nor  shall  he  be  obliged  to  replace  cracks  in 
the  surface,  unless  they  have  resulted  in  the  disintegration  of 
the  surface. 


CEMENT  CURB  AND  GUTTER. 

Cement  curb  and  gutter  shall  be  composed  of  concrete  formed 
as  follows: 

One  (1)  part  of  Portland  cement. 

Three  (3)  parts  of  clean  sharp  sand,  or  other  suitable  material. 

Five  (5)  parts  of  crushed  stone. 

Cement  and  Sand. — Cement  and  sand  shall  be  equal  to  the 
materials  hereinbefore  described  for  use  in  concrete  foundation. 

Stone. — The  crushed  stone  shall  be  clean,  free  from  dirt,  and 
crushed  to  such  size  as  to  measure  not  more  than  one  (1)  inch  in 
any  dimension.  It  shall  be  deposited  at  the  site  of  the  work  in 
such  manner  as  to  insure  its  cleanliness. 

Foundation. — The  curb  and  gutter  composed  of  the  above 
materials  shall  rest  on  a  foundation  of  cinders  six  (6)  inches  in 
thickness  after  being  thoroughly  compacted  by  ramming. 


SPECIFICATIONS.  447 

Dimensions.  —  The  gutter  flag  shall  be  eighteen  (18)  inches 
wide  and  five  (5)  inches  thick;  the  curb  shall  be  six  (6)  inches 
thick  throughout,  except  at  the  upper  face  corner,  which  is  to 
be  rounded  to  a  radius  of  one  and  one-half  (1£)  inches.  The 

height  of  the  curb  above  the  gutter  flag  shall  be inches,  all 

as  shown  on  plans. 

Finish. — All  exposed  surfaces  shall  be  covered  with  a  finish- 
ing coat  of  mortar  three-eighths  (f)  inches  in  thickness,  composed 
of  one  (1)  part  of  cement  thoroughly  mixed  with  one  and  one- 
half  (1J)  parts  of  sand. 

Before  the  concrete  sets,  the  curb  and  gutter  shall  be  cut  into 
sections  not  exceeding  six  (6)  feet  hi  length. 

Construction. — The  curb  and  gutter  as  hereinbefore  described 
shall  be  constructed  at  the  grade  and  to  lines  established  by  the 
Engineer,  . . .  .feet  from  and  parallel  with  the  centre  line  of  the 
street,  except  at  intersections  of  streets  and  alleys,  at  which  points 
it  shall  be  returned  to  the  street  line,  the  necessary  circular  sec- 
tions being  built  to  radii  established  by  the  Engineer.  The  curb 
shall  be  properly  back-filled  to  the  top  thereof. 

PROPOSALS. 

Bidders  will  be  required  to  make  proposals  on  blank  forma 
furnished  by  the  Engineer,  wrhich  proposals  shall  state: 

A  price  per  cubic  yard  for  excavation; 

A  price  per  cubic  yard  for  embankment  or  filling; 

A  price  per  cubic  yard  for  hauling  excavated  material  or 
material  for  use  in  embankment,  for  each  1000  feet  hi  excess  of 
one-half  mile; 

A  price  per  lineal  foot  for  straight  combined  curb  and  gutter; 

A  price  per  lineal  foot  for  circular  combined  curb  and  gutter. 

An  inclusive  price  for  asphalt  pavement,  including  foundation, 
open  or  close  binder,  and  wearing  surface,  together  with  main- 
tenance for  a  period  of ...  .years.1 

1  Attention  must  be  called  to  the  fact  that  propositions  for  the  use  of 
one  kind  of  binder  alone  and  one  type  of  filler  alone  should  be  preferably 
specified  for  any  one  street.  If  th^y  are  both  specified,  there  should  be  some 
provision  for  alternative  bidding. 


448  THE  MODERN    ASPHALT    PAVEMENT. 

An  inclusive  price  for  bituminous  concrete  pavement,  in- 
cluding foundation  and  a  bituminous  concrete  surface,  \yith 
maintenance  for  a  period  of.. .  .years.1 

Other  Specifications. — Specifications  of  another  type  will  be 
found  in  the  appendix,  those  issued  by  Kansas  City  being  char- 
acterized by  demanding  an  asphalt  cement  of  a  certain  character 
without  regard  to  the  fine  material  from  which  it  is  made,  and  are,  on 
this  account,  much  to  be  recommended  from  many  points  of  view. 

Clay  Soils  in  Cold  Climates. — Although  the  preceding  speci- 
fications are,  as  has  been  said,  satisfactory  in  the  majority  of 
instances  there  are  cases  where,  owing  to  the  character  of  the 
climate,  sub-soil,  or  heavy  traffic  to  be  carried  by  the  pavement, 
special  provisions  must  be  made.  On  clay  sub-soil  in  cold  climates 
some  special  provisions,  such  as  are  made  in  Manitoba,  may  be 
desirable  in  the  treatment  of  the  sub-soil  base.  Such  a  provision 
may  be  outlined  as  follows: 

In  clay  soils  trenches  shall  be  dug  across  the  line  of  the  street 
from  the  centre  to  the  trenches  in  which  the  curb  is  laid  on  each 
side  of  the  street,  to  a  depth  of  six  (6)  inches  and  filled  with  broken 
stone  or  large  gravel.  The  entire  roadbed  will  then  be  thor- 
oughly rolled  with  a  steam  roller,  having  a  tread  of  at  least  (60) 
inches  and  a  pressure  per  linear  inch  of  tread  of  at  least  310  pounds, 
along  the  large  roll,  until  it  is  compacted.  All  soft  spots  which 
are  developed  should  be  refilled  and  rerolled.  The  surface  thus 
prepared  must  conform  closely  to  the  prescribed  cross-section  of 
the  street. 

Upon  this  foundation,  broken  stone,  preferably  the  run  of 
crusher,  gravel  or  clean  sand,  will  be  laid  to  the  depth  of  three 
(3)  inches  and  thoroughly  consolidated  by  rolling,  to  be  followed 
by  the  hydraulic  concrete,  the  latter  in  this  way  not  being  brought 
in  contact  with  the  soil  and  drainage  being  provided  by  the  broken 
stone. 

This  form  of  construction  is  most  necessary  in  very  cold  climates 
and  especially  on  clay  soils  where  a  thaw  is  apt  to  occur  from 
the  action  of  frost,  and  where  cracks  have  been  observed  to  open 
in  the  ground  and  extend  through  the  concrete  and  the  asphalt 
surface. 

1  See  footnote  on  page  447. 


SPECIFICATIONS.  449 

As  an  additional  precaution  under  such  conditions  the  follow- 
ing provisions  are  made  as  to  setting  the  curb: 

Curbing. — Curb  of  the  character  described  shall  be  set  hi  con- 
crete hi  a  trench. ..  .niches  deep,  the  bottom  of  which  is  filled 

with  broken  stone  to   a  depth   of inches,  connected  with  the 

broken  stone  cross  trenches  of  the  base,  upon  which  shall  rest 
the  concrete  foundation  for  the  curbstone,  not  less  than  six  (6) 
inches  thick  and  seventeen  (17)  inches  wide,  made  of  the  mate- 
rials in  the  proportions  previously  described  for  the  concrete  base, 
except  that  the  stone  shall  not  exceed  one  and  one-quarter  (1J) 
niches  hi  maximum  dimension.  The  curb  shall  be  imbedded 
immediately  hi  the  centre  of  this  concrete  and  backed  up  with 
additional  concrete  for  a  width  of  six  (6)  inches,  extending  from 
the  concrete  base  to  within  four  (4)  inches  of  the  top  of  the  curb. 
The  broken  stone  underlying  the  concrete  shall  be  graded  to  catch- 
basins  for  the  removal  of  ground-water. 

Sandy  Soils. — On  sandy  soils  at  the  seashore,  where  it  is  diffi- 
cult to  compact  the  sand  under  the  roller,  it  may  be  provided 
that  a  course  of  one  (1)  or  two  (2)  inches  of  gravel  or  other  suit- 
able material  may  be  spread  and  rolled  over  the  sand  before  the 
concrete  foundation  is  constructed 

Asphalt. — While,  in  the  author's  opinion,  there  is  no  question 
that  the  best  asphalt  surface,  in  the  present  state  of  the  industry,  can 
be  constructed  with  Trinidad  lake  asphalt  orgilsonite,  he  would  not 
be  understood  to  affirm  that  satisfactory  work  cannot  be  done  with 
other  bitumens,  and  for  streets  of  light  traffic  the  Engineer  may 
exercise  such  choice  as  he  may  believe  to  be  desirable  from  the 
point  of  view  of  competition.  He  should,  however,  bear  in  mind 
that  the  skill  which  the  contractor  may  possess  and  his  knowl- 
edge of  the  art  of  constructing  an  asphalt  pavement  is  of  as  great 
importance  as  the  materials  in  use  or  the  price  which  may  be  bid. 
At  an  equal  cost  the  pavement  constructed  with  skill  and  intelli- 
gence may  be  worth  a  very  much  larger  sum  when  completed 
than  another  surface  carelessly  constructed.  These  points  should 
weigh  largely  hi  the  awarding  of  contracts  if  the  cost  of  main- 
tenance of  the  surface  to  the  city  after  the  expiration  of  the  guar- 
antee period  is  to  be  considered. 


450 


THE    MODERN    ASPHALT    PAVEMENT. 


Grades  of  Streets  on  which  Asphalt  Pavements  may  be  Con- 
structed.— The  general  impression  has  gained  ground,  very  natu- 
rally, that  asphalt  pavements  are  unsuited  to  grades  of  more  than 
4  to  5  per  cent.  That  this  is  an  erroneous  conclusion  may  be  seen 
from  the  fact  that  in  1890  an  asphalt  surface  was  laid  in  Wash- 
ington, D.  C.,  on  Thirty-fourth  Street,  N.  W.,  from  M  Street  to 
Prospect  Street,  275  feet  long,  the  grade  of  which  is  9.74  per  cent, 
and  that  in  Kansas  City,  Mo.,  the  following  streets  have  been  con- 
structed with  the  grades  given.1 

GRADES  IN  KANSAS  CITY,  MO.,  FOR  ASPHALT  PAVEMENTS. 


Year  Laid. 

Street. 

Grade. 

1898 

Jefferson  Street   18  to  20. 

12  5% 

1895 
1897 
1895 

11  Street,  Maine  to  Wyandotte.  . 
Troost  Ave.,  19  to  Belt  Line.  .  .  . 
Central  Street,  16  to  17  

7.5 

8.0 
10  0 

1894 

Forest  Ave.,  Independence  to  8. 

8.0 

All  of  these  streets  are  in  constant  use  and  are  satisfactory 
except  on  occasions  where  a  thin  coating  of  moisture  has 
become  congealed  on  the  surface.  Several  of  the  streets  in  Kan- 
sas City  are  only  paved  with  asphalt  in  the  centre,  the  sides 
having  a  stone  or  brick  surface.  Nevertheless,  the  asphalt  sur- 
face is  universally  used  in  preference  to  the  brick  or  stone,  and 
appears  to  be  no  more  slippery  even  under  the  most  trying  con- 
ditions. Where  a  film  of  ice  causes  asphalt  to  be  slippery  traffic 
is  diverted  to  other  streets  with  lighter  grades,  rather  than  to  the 
brick  or  stone.  As  a  matter  of  fact  the  limiting  conditions  in 
determining  the  extent  to  which  the  steepness  of  a  grade  will 
prevent  the  use  of  an  asphalt  surface  mixture  will  depend  entirely 
upon  the  climate  and  the  nature  of  the  traffic  which  uses  the  street. 
Eight  per  cent  is  not  an  excessive  grade  under  ordinary  eastern 
conditions,  while  in  a  climate  like  Seattle,  Wash.,  a  10  per  cent 
or  12  per  cent  grade  is  quite  possible. 

1  Tillson  cites  a  grade  of  17  per  cent  on  a  portion  of  Bates  Street,  in 
Pittsburg,  Pa.,  and  12£  per  cent  in  Scranton,  while  Baker  mentions  one  of 
16  per  cent  in  San  Francisco,  Cal. 


SPECIFICATIONS. 


451 


Crown  or  Camber. — That  an  asphalt  pavement  should  show 
in  transverse  section  a  proper  profile  for  the  surface  is  as  important 
as  that  the  grade  should  be  sufficient  to  provide  for  proper  drain- 
age. There  is  little  agreement  among  engineers  in  regard  to 
what  this  proper  form  should  be,  but  it  is  quite  certain  that  the 
tendency  in  America  is  to  make  all  the  asphalt  pavements  much 
too  flat.  Theoretically,  no  doubt,  an  asphalt  pavement  should 
demand  but  a  low  crown  or  camber.  In  practice,  however,  the 
pavement  will  prove  much  more  satisfactory  and  pleasing  to 
the  eye  if  this  is  maintained  at  a  comparatively  high  figure,  since 
in  wet  weather  the  slight  depressions  which  it  is  impossible  to 
avoid  in  laying  such  a  surface,  or  which  are  formed  by  unequal 
compression  and  traffic,  will  not  then  be  revealed  as  small  pools 
of  water.  This  is  especially  the  case  if  the  profile  of  the  surface 
shows  a  plane  surface  from  the  gutter  to  the  crown  instead  of  a 
curve. 

It  is  generally  assumed  that  for  a  roadway  30  feet  wide  a 
crown  of  4  inches  should  be  adopted,  with  a  curve  towards  the 
gutter  having  a  somewhat  greater  fall  near  the  latter  and  decreas- 
ing towards  the  crown.  The  objection  to  this  profile  is  that  the 
street  is  too  flat  on  the  crown,  with  the  result  that  depressions  form 
there  which  retain  water.  It  is,  therefore,  much  better  to  keep 
the  crown  raised  sufficiently  to  avoid  this.  On  the  other  hand, 
with  a  nearly  flat  crown,  the  centre  of  the  street  which  is  used 
principally  for  traffic  is  of  a  more  acceptable  form.  Mr.  G.  W. 
Tillson  l  gives  the  following  table  showing  the  necessary  crown 
for  streets  of  a  width  from  24  to  60  feet. 


Width  of  roadway     .    ... 

24  ft. 

30  ft. 

30  ft. 

36  ft. 

48  ft. 

60  ft. 

Crown.  ...          

3  ins. 

4  ins. 

6  ins. 

5  ins. 

6  ins. 

8  ins. 

Fall  towards  gutter  in  cen- 
tral J  of  roadway  
Rate  per  100  
Fall  towards  gutter  in  sec- 
ond J  of  roadway.  . 

Jin. 

8£  ins. 

1  in. 

4  in. 

9  ms. 

1^  ins. 

§  in. 
13£  ins. 

2  ins. 

f  in. 
9i  ins. 

1§  ins. 

f  in. 
8£  ins. 

2  ins. 

f  in. 
8|  ins. 

2|  ins. 

Rate  per  100 

9'    1" 

2'  3" 

3'  4" 

2/  4// 

2'  1" 

2'  3" 

Fall  to  gutter  in  £  of  road- 
way adjacent  to  curb.  . 
Rate'per  100.  . 

1  §  ins. 
3'  6" 

2f  ins. 
3'  8" 

3£  ins. 
5'  6" 

21  ins. 
3'  3" 

3J  ins. 
3'  6" 

4f  ins. 
3'  9" 

1  Street  Pavements  and  Paving  Materials,  202. 


452 


THE  MODERN  ASPHALT  PAVEMENT. 


The  author  would  regard  an  8-inch  crown  as  none  too  high 
for  a  60-foot  roadway,  while  on  many  flat  streets  a  6-inch  crown 
is  not  too  high  for  a  30-foot  roadway.  Of  course  the  steeper  the 
grade  of  the  street  the  smaller  the  height  of  crown  which  is 
necessary,  and  this  fact  does  not  seem  to  have  been  taken  into 
consideration  in  the  table  which  Tillson  offers. 

In  Paris,  France,  the  crown  for  asphalt  streets  is  determined 
by  the  formula,  Fig.  26. 

Provision  is  made  for  a  drop  of  10  per  cent  from  the  point  A 
towards  the  curb  for  a  space  of  50  cm.  (19.7  inches).  This  latter 
provision  seems  to  the  author  to  be  an  excellent  one  and,  from 
his  experience  in  Paris,  the  form  of  street  profile  to  be  a  very  suc- 
cessful one. 

Baker l  gives  a  resume  of  the  specifications  of  various  cities 


FIG.  26. 


ATL2 
'NL-l' 
AB=  0.05  meters. 

for  crowns  of  asphalt  pavements  to  which  the  reader  may  refer. 
The  provisions  of  the  City  of  Omaha  are  also  very  excellent. 

1  Roads  and  Pavements,  348. 


SPECIFICATIONS. 


453 


TABLE  OF  STANDARD  CROWNS. 
(City  Engineers  Office,  Omaha,  Neb.,  1902.) 


Crowns  for  American  Sheet  Asphalt  Pavement  in  Feet. 

Distance 

Grade  of  Street. 

Between 

Curbs. 

1 

1 

1% 

2% 

3% 

4% 

5% 

6% 

7% 

8% 

9% 

10% 

11% 

12% 

20  feet  .  .  . 

.40 

.38 

.37 

.35 

.34 

.32 

.30 

.29 

.27 

.26 

.24 

.22 

.21 

25 

.50 

.48 

.46 

.44 

.42 

.40 

.38 

.36 

.34 

.32 

.30 

.28 

.26 

30 

.60 

.58 

.55 

.53 

.50 

.48 

.46 

.43 

.41 

.38 

.36 

.34 

.31 

35 

.70 

.67 

.64 

.62 

.59 

.56 

.53 

.50 

.48 

.45 

.42 

.39 

.36 

40 

.80 

.77 

.74 

.70 

.67 

.64 

.61 

.58 

.54 

.51 

.48 

.45 

.42 

45 

.90 

.86 

.83 

.79 

.76 

.72 

.68 

.65 

.61 

.58 

.54 

.50 

.47 

50 

1.00 

.96 

.92 

.88 

.84 

.80 

.76 

.72 

.68 

.64 

.60 

.56 

.52 

55 

1.10 

1.06 

1.01 

.97 

.92 

.88 

.84 

.79 

.75 

.70 

.66 

.62 

.57 

60 

1.20 

1.151.10 

1.06 

1.01 

.96 

.91 

.86 

.82 

.77 

.72 

.67 

.62 

65 

1.30 

1.2511.20 

1.14 

1.09 

1.04 

.99 

.94 

.88 

.83 

.78 

.73 

.68 

70 

1.40 

1.341.29 

1.23 

1.18 

1.12 

1.06 

1.01 

.95 

.90 

.84 

.78 

.73 

75 

1.50 

1.  4411.  38 

1.32 

1.26 

1.20 

1.14 

1.08 

1.02 

.96 

.90 

.84 

.78 

80 

1.60 

1.54 

1.47 

1.41 

1.34 

1.28 

1.22 

1.15 

1.09 

1.02 

.96 

.90 

.83 

NOTE. — The  formula  used  for  the  construction  of  the  table  is  as  follows : 

TF(100-4/). 

5000 

C — crown  of  pavement  in  feet; 
W  =  distance  between  curbs  in  feet; 
/= number  of  feet  fall  per  100  feet  of  street. 

Note. — Where  the  crown  is  less  than  0.5  foot  make  the  gutter  0.5  foot, 
and  where  it  is  0.7  foot  make  the  gutter  0.7  foot,  and  for  intermediate  crowns 
make  the  gutter  equal  the  crowns. — Andrew  Rosewater,  M.  Am.  Soc.  C.  E., 
City  Engineer. 


None  of  these  methods  of  arriving  at  a  proper  figure  for  crown 
is  applicable  if  opposite  sides  of  the  street  are  not  of  the  same 
elevation. 

The  subject  of  the  form  to  be  given  to  streets  is  discussed  at 
much  length  and  with  reference  to  various  cases  in  ' '  Traite 
Pratique  des  Travaux  en  Asphalte,"  Letouze  etLoyeau,  Paris,  1897, 
and  reference  must  be  made  to  this  work  for  more  detailed  formula 
and  special  applications. 

Gutters. — In  many  cities  where  concrete  curb  and  gutter  are 
not  in  use,  there  has  been  a  tendency  to  use  either  stone  or  brick 


454  THE    MODERN    ASPHALT    PAVEMENT. 

as  a  substitute  for  an  asphalt  surface  in  gutters  of  asphalt  streets. 
From  what  has  been  shown  in  the  previous  pages  it  is  evident 
that  where  the  asphalt-surface  mixture  is  made  on  the  lines  laid 
down  by  the  author,  and  where  the  form  of  construction  employed 
in  the  street  is  such  as  to  provide  satisfactory  drainage,  there  is  no 
reason  why  the  asphalt  surface  should  not  be  carried  from  curb  to 
curb,  nor  is  there  any  necessity  for  painting  such  a  surface  with 
asphalt  or  bitumen,  if  the  mixture  of  which  it  is  composed  is 
constructed  on  modern  lines.  In  the  early  days  of  the  industry 
this  painting  became  the  custom,  owing  to  the  fact  that  the 
mixtures  were  made  with  sand  so  badly  graded  and  so  porous 
that  they  could  not  resist  water  action. 


CHAPTER  XXIIL 
THE   MERITS   OF  THE   MODERN    SHEET-ASPHALT   PAVEMENT. 

WHETHER  a  sheet-asphalt  pavement  possesses  any  lasting  degree 
of  merit  will  depend  entirely  upon  the  manner  in  which  it  is  con- 
structed from  the  base  up,  including  proper  drainage  and  the  charac- 
ter of  the  asphalt  mixture  which  forms  the  surface.  It  has  already 
been  made  evident  that  the  greatest  care  is  necessary  in  all  these 
respects.  It  will  be  only  worth  while,  therefore,  to  consider 
what  the  merits  are  of  a  sheet-asphalt  pavement  of  standard 
construction.  Such  a  pavement  is  desirable  for  the  following 
reasons : 

1.  It  does  not  disintegrate  under  impact  or  attrition,  and  con- 
sequently produces  neither  mud  nor  dust. 

2.  It  can  be  kept  perfectly  clean  if  the  proper  efforts  are  made 
to  do  so. 

3.  It  has  an  impervious  surface  and  does  not  absorb  filthy 
liquids,  as  is  the  case  with  wood  blocks. 

4.  It  affords  the  best  foothold  for  horses  except  under  occa- 
sional conditions. 

5.  Traction  on  such  a  surface  can  be  carried  on  with  a  smaller 
expenditure  of  force  than  on  any  other  form  of  pavement. 

6.  Its  wearing  properties  compare  more  than  favorably  with 
granite  and  exceed  that  of  any  other  form  of  pavement  under 
heavy  traffic. 

7.  Deterioration  hi  a  standard  asphalt  pavement  is  of  a  kind 
that  can  be  readily  and  economically  met  owing  to  the  simplicity 
of  making  repairs,  something  that  cannot  be  done  satisfactorily 
with  any  other  form  of  pavement. 

455 


456  THE  MODERN  ASPHALT  PAVEMENT. 

8.  Cuts  in  the  pavement  for  underground  work  can  be  replaced 
in   a   manner   which  makes   the   repairs   undistinguishable   from 
the  original  surface,  whereas  they  are  quite  evident  in  the  case 
of  other  pavements. 

9.  It  increases  the  actual  and  rental  value  of  all  real  estate 
abutting  on  streets  where  it  is  laid  to  a  larger  extent  than  any 
other  form  of  pavement. 

10.  The  wear  and  tear  upon  horses  and  carriages  is  largely 
reduced  by  asphalt  pavements,  and  it  has  been  estimated  for 
Philadelphia  l  that  the  repairs  to  vehicles  in  that  city  due  to 
rough  pavements  existing  there  in  1885,  which  could  be  saved 
by  sheet-asphalt  pavements,  would  amount  to  $1,000,000  annually. 
The  universal  testimony  of  fire-department  chiefs  is  that  there  is 
far  less  wear  and  tear  to  the  running  gear  of  the  engines,  hose 
carriages  and  trucks  on  asphalt  pavements  than  on  stone  blocks, 
and  consequently  less  liability  to  break  down  or  to  have  acci- 
dents, while  much  better  tune  is  made  in  going  to  fires. 

That  asphalt  pavement  will  sustain  the  heaviest  traffic  that 
is  carried  by  any  street  in  the  world  can  be  seen  from  the  follow- 
ing determination  of  the  number  of  vehicles  and  the  tonnage  on 
Fifth  Avenue  and  some  other  streets  in  New  York  City  during  the 
months  of  November  and  December,  1904.  See  table  on  page  457. 

The  heaviest  traffic  in  London,  as  determined  in  1879,  was 
422  tons  per  foot  of  width  per  day.  The  traffic  on  Fifth  Avenue, 
which  has  been  an  extremely  successful  asphalt  pavement,  is, 
therefore,  equal  to,  if  not  greater  than,  that  sustained  by  the  pave- 
ment on  many  of  the  most  heavily  travelled  streets  of  Europe. 

The  defects  which  have  generally  been  assigned  to  an  asphalt 
pavement  are  its  comparatively  great  first  cost  and  cost  of  main- 
tenance. Its  first  cost  may  be  larger  than  that  of  some  other 
inferior  forms  of  pavement,  but  considering  the  length  of  time 
that  an  asphalt  surface  will  wear,  if  of  standard  construction,  this 
cost  is  smaller  per  annum  and  per  ton  of  traffic  carried  than 
that  of  any  other  form.  The  cost  of  maintenance  has  no  doubt 
been  large  for  many  pavements  constructed  in  the  past  and  will 
be  large  for  many  constructed  in  the  future  which  are  not  of  stand- 

1  The  Philadelphia  North  American,  Oct.  12,  1885. 


MERITS  OF  THE  MODERN  SHEET-ASPHALT  PAVEMENT.  457 


ard  composition.  With  the  best  form  of  construction  the  cost 
per  yard  will  not  be  excessive  and  the  public  will  have  the  advan- 
tage, if  the  city  maintains  its  streets,  which  unfortunately  is  not 
always  the  case,  of  having  a  perfect  pavement  at  all  periods  of 
its  existence,  instead  of  one  which  becomes  worse  and  worse  with 
each  year  of  its  age. 

Another  defect  has  been  said  to  be  the  fact  that  it  is  unsuited 
for  steep  grades.  From  the  figures  given  on  pages  450  and  451 
it  is  evident  that  this  is  not  so. 

There  can  be  no  question  that  a  standard  sheet-asphalt  pave- 
ment possesses  more  merits  than  any  other,  and  fewer  defects. 
It  is  undoubtedly  the  pavement  of  the  present  and  of  the  future. 

TRAFFIC  RECORD  TAKEN  ON  STREETS  PAVED  WITH  ASPHALT 
IN   NEW  YORK,  N.  Y.,  NOVEMBER  AND  DECEMBER,  1904. 


Tonnage 
11  Hours. 

Average 
Tonnage 
per  Linear 
Foot  of 
Width  per 
11  Hours. 

Average 
Tonnage 
per  Hour. 

Average 
Number  of 
Vehicles 

11  Hours. 

Average 
Tonnage 

Vehicle. 

Fourth  Street,  from  Wooster 
to  West  Broadway 

9254  22 

289    18 

841  35 

3394 

2  73 

Eighth  Avenue,  from  35th 
to  36th  Streets  
Thirty-fourth   Street,   from 
Broadway  to  Seventh  Av  . 
First  Avenue,  from  26th  to 
27th  Streets  .  .  . 

13024.52 
2176.60 
19253  76 

296.02 
89.22 
435  58 

1184.05 
197.86 
1750  34 

5720 
1072 
6034 

2.28 
2.03 
3  18 

Fifth  Avenue,  from  33d  to 
34th  Streets.  .  .  . 

19274  47 

481  85 

1752  20 

11787 

1  64 

Broadway,  from  18th  to  19th 
Streets  

7491  70 

299  63 

681  06 

3817 

1  97 

The  Cost  of  Asphalt  Pavements. — No  general  statement  can 
be  made  in  regard  to  the  cost  of  an  asphalt  pavement,  as  it  is  a 
function  of  too  many  variables ;  these  variables  can,  however,  be 
considered  individually.  They  are: 

1.  Freight  rates  for  the  transportation  of  the  plant  and  mate- 
rials of  construction  to  the  locality  where  the  pavement  is  to 
be  laid. 

2.  Local  cost  of  materials  of  construction,  such  as  sand,  cement, 
gravel,  broken  stone,  and  filler. 


458  THE  MODERN  ASPHALT  PAVEMENT. 

3.  The  cost  of  local  labor. 

4.  The  form  of  construction  which  is  specified. 

5.  The  character  of  the  traffic  which  the  street  is  to  carry, 
its  grade,  and  the  character  of  the  pavement  on  adjoining  streets. 

6.  The  period  of  guarantee  demanded. 

7.  The  terms  of  payment. 

With  so  many  changeable  conditions  it  would,  of  course,  be 
impossible  to  give  any  general  data  as  to  the  cost  of  an  asphalt 
pavement.  It  may  vary  from  $4  or  $5  per  yard  on  a  street  of 
extreme  traffic  in  a  large  city  which  is  guaranteed  for  15  years, 
and  $1.25  per  yard  on  old  brick  pavement  for  the  base  where 
the  traffic  is  very  light,  as  in  a  residence  street  or  where  no  guar- 
antee is  demanded,  as  is  the  case  in  the  State  of  California. 

Cost  of  Maintenance. — The  cost  of  maintenance  is  quite  as 
uncertain  an  element  as  the  cost  of  construction;  and  even  more 
so,  since  it  will  depend  not  only  on  the  character  of  the  original 
work  but  upon  the  amount  of  attention  which  is  given  by  the 
company  constructing  the  pavement,  or  by  the  authorities  after 
the  former's  guarantee  has  expired,  to  keeping  the  surface  in  first- 
class  condition.  If  it  is  neglected  the  cost  of  maintenance  may 
become  large,  whereas  if  carefully  kept  up  this  may  well  be  small. 

The  character  of  the  base  which  supports  the  pavement  will 
have  more  to  do  with  the  cost  of  its  maintenance,  if  the  surface 
is  a  standard  one,  than  any  other  controlling  condition.  In  the 
observation  of  the  writer  at  least  90  per  cent  of  all  maintenance 
work  on  asphalt  pavements  with  well-constructed  surfaces  is  due 
to  weakness  and  deficiency  in  the  base. 

It  is  of  interest  in  this  connection,  however,  to  note  the  data 
contained  in  a  paper  by  Capt.  H.  C.  Newcomer,  Corps  of  Engineers, 
United  States  Army,  in  regard  to  the  cost  of  maintenance  of  the 
asphalt  pavement  in  Washington,  D.  C.,  especially  as  the  sur- 
face mixtures  laid  in  that  city  have  been,  unfortunately,  not  of 
standard  quality,  owing  to  deficiencies  in  the  character  of  the 
local  sand  supply.  Capt.  Newcomer  has  found  l  that  "  the  aver- 
age cost  per  square  yard  per  annum  for  the  second  five-year  period 
of  the  life  of  the  pavements  considered  was  1.65  cents;  for  the 

1  Engineering  News,  1904,  Feb.  18,  51,  165. 


MERITS  OF  THE  MODERN  SHEET-ASPHALT  PAVEMENT.   459 

third  five-year  period,  3.37  cents;  for  the  fourth  five-year  period, 
3.78  cents,  and  for  the  fifth  five-year  period,  2.56  cents.  The 
average  cost  for  all  ages  tabulated  was  2.8  cents." 

It  is  worthy  of  note  in  this  connection  that  of  the  2,425,732 
square  yards  of  bituminous  pavements  of  all  kinds,  including  coal- 
tar,  in  the  preceding  estimate,  many  of  which  were  very  inferior, 
not  less  than  2,161,181  square  yards  were  constructed  of  Trinidad 
asphalt. 


CHAPTER  XXIV. 
ACTION   OF   WATER   ON   ASPHALT   PAVEMENTS. 

THE  action  of  water  on  asphalt  and  on  asphalt  pavements 
has  been  a  prominent  topic  of  discussion  from  the  early  days  of 
the  industry,  and  the  subject,  for  many  reasons,  remains  one  of 
peculiar  interest  to-day,  since  many  mistaken  ideas  in  regard 
to  it  are  still  in  vogue. 

Asphalt  surface  mixtures,  the  mineral  aggregate  of  which  is 
not  properly  graded  and  balanced  and  which,  in  consequence, 
lack  density  and  an  impervious  surface,  are  attacked  by  water 
when  subjected  to  its  continued  action,  from  lack  of  proper  drain- 
age or  other  reasons,  without  regard  to  the  nature  of  the  asphalt 
of  which  the  mixture  is  made,  although  under  these  conditions 
one  asphalt  may  be  attacked  more  than  another.  With  the  stand- 
ard surface  mixture  constructed  on  the  ideas  laid  down  by  the 
author  in  the  previous  pages  surface  mixtures  may  be  constructed 
of  any  asphalt  which  are  equally  resistant  to  water  action,  but 
all  of  which  are  attacked  more  or  less  by  the  water  unless  allowed 
to  dry  out  at  intervals.  In  a  properly  constructed  pavement  no 
important  deterioration  from  water  action  should  ensue  within 
the  life  of  the  pavement  and,  as  a  matter  of  fact,  in  the  author's 
experience,  the  deterioration  in  the  asphalt  surfaces  laid  under 
his  supervision  has  in  the  last  ten  years  become  an  item  which 
is  hardly  worth  consideration,  where  the  form  of  construction 
has  provided  satisfactory  drainage. 

As  it  must  be  admitted  that  asphalts  are  attacked  by  water 
to  different  degrees  when  the  mixtures  are  not  dense,  and  espe- 
cially in  laboratory  tests,  it  is  of  interest  to  examine  into  the  rea- 

460 


ACTION  OF  WATER  OX  ASPHALT  PAVEMENTS.          461 

son  for  this,  in  order  that  we  may  be  able  to  compare  practical 
results  with  those  obtained  by  experiment  and  determine  the 
means  for  preventing  such  action  on  pavements  actually  in  use. 

Numerous  observers  have  detected  and  noted  the  fact  that 
there  is  a  difference  in  the  degree  to  which  water  acts  upon  vari- 
ous asphalts  and  fluxes.  Messrs.  Whipple  and  Jackson  have  made 
an  elaborate  investigation  of  the  subject,  the  results  of  which 
were  presented  in  a  paper  read  before  the  Brooklyn  Engineers' 
Club  in  March,  1900,  which  was  published  in  the  Engineering 
News  for  March  22,  1900.  These  results,  although  of  little  inter- 
est as  showing  the  effect  of  water  on  a  well-constructed  asphalt 
paving  mixture,  since  the  pure  bitumens  were  themselves  exposed 
by  these  investigators  directly  to  the  continued  action  of  water 
in  order  to  determine  their  relative  value  for  the  construction  of 
concrete  lining  for  reservoirs  and  not  for  pavements,  are  of  inter- 
est as  showing  that  experiments  conducted  under  conditions 
employed  by  these  investigators  may  lead  to  conclusions  which 
are  utterly  erroneous  as  applied  to  the  paving  industry,  except 
when  the  asphalts  in  question  are  used  in  an  unskillful  way. 

Actual  Results  on  the  Streets. — It  is  of  interest  to  consider 
what  the  practical  experience  has  been  on  the  street  during 
the  last  fifteen  years  as  regards  the  action  of  water  on  asphalt 
surface  mixtures.  In  the  early  days  of  the  industry,  as  has  already 
appeared,  the  asphalt  surface  mixtures  were  very  open.  At  the 
time  that  the  author  was  connected  with  the  Engineer  Department 
of  the  District  of  Columbia  the  Trinidad  asphalt  surface  mixtures 
were  constructed  with  coarse  sand  and  very  little  filler.  The 
gutters  of  streets  which  were  paved  with  mixtures  of  this  descrip- 
tion were  much  given  to  deterioration  from  the  action  of  water, 
and  the  same  conditions  were  met  in  other  cities,  so  that  at  that 
time  every  one  believed  that  it  would  be  impossible  to  construct 
a  Trinidad  surface  mixture  which  would  not  be  attacked  by  water. 
This  idea  has  persisted  in  the  minds  of  many  who  have  not  followed 
the  industry  carefully  down  to  the  present  day,  and  it  was  only 
dissipated  in  the  author's  mind  by  an  experience  extending  from 
1894  to  1896  during  an  attempt  to  introduce  the  American  form 
of  asphalt  pavement  in  London,  England.  In  1894  a  Trinidad 


432  THE   MODERN  ASPHALT   PAVEMENT. 

asphalt  surface  was  constructed  on  Pelham  Street,  Kensington, 
and  on  King's  Highway,  Chelsea,  in  London,  using  Trinidad  asphalt 
in  much  the  same  way  that  he  had  employed  it  in  previous  years 
in  Washington,  D.  C.,  the  modern  methods  of  constructing  a 
mixture  to  withstand  heavy  traffic  and  wet  climate  not  having  been 
developed  at  that  time.  The  results  were  that  the  pavements 
were  not  an  entire  success  and  scaled.  It  was  suggested  that 
this  was  due  to  the  fact  that  the  asphalt  in  use  was  Trinidad  and 
that  this  was  constantly  attacked  by  the  continuous  fogs  of  London. 
The  pavements  were,  therefore,  replaced  in  the  following  year 
with  a  mixture  made  with  Bermudez  asphalt.  These  surfaces 
went  to  pieces  much  more  rapidly  than  the  previous  Trinidad 
surfaces.  By  this  time  the  principles  which  have  been  elucidated 
in  the  preceding  pages  had  been  largely  worked  out.  In  the  third 
year  Trinidad  asphalt  surfaces  were  laid  in  London  on  these  lines 
which  not  only  were  not  attacked  by  the  continued  wet  weather 
and  fogs  of  that  climate,  but  which  have  remained  there  to  the 
present  time,  having  shown  no  deterioration  due  to  water  action. 
If  the  Bermudez  surfaces  had  been  constructed  with  the  same 
regard  to  the  mineral  aggregate  and  to  the  character  of  the  asphalt 
cement  prepared  from  it  they  would  undoubtedly  have  shown 
an  equal  freedom  from  the  action  of  water,  but  it  is  not  probable 
that  they  would  have  shown  an  equal  resistance  to  the  deteriorating 
influence  of  the  heavy  traffic  on  the  streets  on  which  the  pavements 
were  laid.  Practical  experience  rather  than  theory,  therefore,  leads 
the  author  to  conclude  that  an  asphalt  which  may  not  appear  to  be 
as  satisfactory  in  laboratory  tests  may  prove  more  so  in  actual 
construction. 

That  asphalts  which  are  not  attacked  by  water  in  the  laboratory 
may  be  seriously  affected  by  it  in  asphalt  surface  mixture  has 
frequently  been  revealed,  but  never  in  a  more  striking  way  than 
in  Reading,  Pa.,  where  house  drainage  is  conducted  along  the 
gutters  of  the  Bermudez  asphalt  pavements  of  that  town,  in  con- 
sequence of  which  they  have  entirely  disintegrated,  as  shown  in 
the  accompanying  illustration,  Fig.  27. 

It  appears  then  that  it  is  the  manner  in  which  the  asphalt  is 
used  and  the  practical  results  obtained  with  it  rather  than  its 


DO 

~ 
_z 

J* 


464 


THE  MODERN   ASPHALT  PAVEMENT. 


properties  as  revealed  by  laboratory  tests  which  should  control 
our  judgment  in  forming  an  opinion  of  its  behavior  towards  water 
in  an  asphalt-surface  mixture  on  the  street.1 

As  a  practical  example  of  the  difference  between  surface  mix- 
tures actually  in  use  and  made  with  different  asphalts  in  their  rela- 
tion to  water  absorption  in  the  laboratory,  the  results  of  an  examina- 
tion of  the  Trinidad  and  Bermudez  surface  mixtures  which  were 
being  laid  in  the  city  of  New  York  in  the  year  1904  may  be  of 
interest.  These  mixtures  consisted  of  the  following  material.*  ^ 
the  proportions  given  and  had  the  following  composition ' 


Proportions. 

Trinidad. 

Bermudez. 

Sand  (1  Cow  Bay  and  1  Grossman) 
Filler  (P  C  dust)   . 

74.7% 
9  6 

73.7% 
14  8 

Asphalt  cement.  .  . 

15  7 

11  5 

Analyses. 
Bitumen.  ...           

100.0 
11  0% 

100.0 

11  2% 

16  0 

17  8 

100-    '  '              

11.0 

12  0 

80-                    

11.0 

10.0 

50- 

24  0 

27.0 

40- 

13  0 

12.0 

30-                        .    . 

7  0 

5  0 

20-                   

4  0 

3  0 

10-                   

3  0 

2  0 

100.0 

100.0 

Of  the  above  mixtures  cylinders  1  inch  in  height  were  made 
having  the  greatest  density  possible,  by  compressing  them  under 
impact  in  a  diamond  mortar  of  a  diameter  of  1.25  inches.  The 
cylinders  of  mixtures  had  the  following  densities  and  weight: 


1  This  subject  has  been  discussed  at  length  in  the  Engineering  News, 
1904,  June  2,  51,  520. 


ACTION  OF  WATER  ON  ASPHALT  PAVEMENTS. 


465 


Cylinder 
Number. 

Trinidad. 

Bermudez. 

Density. 

Weight 
(Grams). 

Density. 

Weight 
(Grams). 

1 

2.247 
2.200 
2.204 
2.217 
2.214 
2.223 

2.217 

47.522 
47.227 
46.963 

46.885 
48.536 
49.548 

47.780 

2.262 
2.225 
2.232 

2.277 
2.222 
2.260 

2.246 

46.728 
47.410 
47.551 
49.631 
49.410 
52.257 

48.831 

2  

3  

4  

5 

6 

Average. 

These  cylinders  were  exposed  to  the  action  of  running  water 
for  a  length  of  time.  The  gain  in  weight  of  the  cylinders  at  various 
intervals  is  shown  in  the  following  table  in  fractions  of  a  pound  per 
square  yard : 

ABSORPTION  OF  WATER.      POUNDS  PER  SQUARE  YARD. 


Cylinder 
Number. 

Trinidad. 

Bermudez. 

1 
Week 

4 
Weeks. 

2 

Months. 

3 

Months. 

Week. 

4 
Weeks. 

2 

Months. 

3 
Months 

1.. 
2  ....  . 

.0849 
0789 
.0763 
.0869 
.0839 
.0706 

.0803 

.1111 
.1009 
.0991 
.1069 
.1066 
.0943 

.1031 

.1262 

.1190 
.1149 
.1199 
.1237 
.1137 

.1196 

.1291 
.1194 
.1171 
.1240 
.1254 
.0914 

.1177 

.0961 
.1485 
.0868 
.0894 
.0909 
.0526 

.0940 

.1020 
.1428 
.0914 
.0883 
.0966 
.0566 

.0963 

.1183 
.1640 
.1134 
.1077 
.1198 
.0746 

.1163 

.1174 
.1694 
.1103 
.1089 
.1194 
.0729 

.1164 

3  
4..  .... 

5.  
6. 

Average. 

After  an  exposure  of  three  months  none  of  the  cylinders 
showed  any  signs  of  softening.  Those  containing  Bermudez 
asphalt  could,  however,  be  distinguished  from  those  made  with 
Trinidad  asphalt  by  slight  excrescences  the  size  of  pin-heads, 
which  had  appeared  upon  the  surface.  Fig.  28.  It  must  be 
remembered,  too,  that  the  cylinders  were  not  prepared  from  mix- 
tures made  in  the  laboratory,  but  were  made  from  material  which 
was  actually  being  used  on  the  street. 


466 


THE  MODERN  ASPHALT  PAVEMENT. 


When  pieces  of  glass  were  coated  with  Trinidad  and  Bermudez 
asphalt  cement  and  with  one  made  from  a  California  residual  pitch 
and  immersed  in  running  water  for  a  week  they  were  all  more  or 
less  attacked  thereby,  as  can  be  seen  from  the  accompanying 
illustration,  Fig.  29.  From  the  preceding  results  it  is  apparent 


Trinidad  Lake  Asphalt,  Bermudez  Asphalt. 

Surface  Mixture. 

In  running  water  five  months. 

FIG.  28. 

at  once  that  although  all  asphalts  under  certain  circumstances 
are  attacked  by  water,  Trinidad  asphalt  when  properly  used  in  an 
asphalt  surface  mixture  is  the  equal  of  any  other  in  resisting 
power,  and  this  fact  being  proved  to  a  contractor's  satisfaction,  he 


California  Oil 
Asphalt  Cement. 


Bermudez 

Asphalt  Cement. 

In  running  water  one  week. 

FIG.  29. 


Trinidad  Lake 
Asphalt  Cement. 


ACTION  OF  WATER   ON  ASPHALT  PAVEMENTS.  467 

prefers  to  employ  it  for  the  many  reasons  which  have  been  given 
in  another  place,  namely,  because  no  other  material  offers  such  a 
uniform  supply  as  that  taken  from  the  Trinidad  pitch  lake,  every 
cargo  being  handled  in  the  same  manner  as  those  preceding  it, 
because  the  bitumen  which  it  contains  is  free  from  hydrocarbons, 
which  are  volatile  at  the  temperature  at  which  it  is  necessary  to 
maintain  a  surface  mixture,  in  consequence  of  which  asphalt  cement 
made  with  it  from  proper  flux  is  peculiarly  non-volatile  and  non- 
changeable  at  this  temperature,  and  because  it  can  be  maintained 
for  a  considerable  length  of  time  at  high  temperatures  without 
hardening  excessively,  even  when  tossed  about  loosely  with  exces- 
sively hot  sand  in  any  process  of  turning  out  the  surface  mixture. 

Cause  of  the  Action  of  Water  on  Asphalt  Under  Certain  Cir- 
cumstances.— All  bitumens,  as  has  been  seen,  are  more  or  less 
acted  upon  by  water  under  certain  conditions.  It  is  a  matter  of 
great  interest  to  determine  what  conditions  are  most  favorable 
for  the  destructive  action  of  water,  how  far  this  action  is  inherent 
in  certain  properties  of  the  bitumen,  and  how  far  to  the  presence 
of  gases  or  salts  soluble  in  water,  or  of  the  latter  mixed  with 
the  asphalt. 

There  has  been  a  great  cry  that  the  soluble  salts  in  Trinidad 
asphalt  were  the  cause  of  the  deterioration  of  this  material  in  the 
presence  of  water.  The  idea  unfortunately  originated  with  the 
author  many  years  ago  on  insufficient  evidence.  It  was  soon  shown 
that  the  addition  of  5  per  cent  of  common  salt  to  a  Trinidad  asphalt 
surface  mixture  or  immersion  of  the  latter  in  salt  water  com- 
pletely prevented  any  disintegration,  even  of  the  old-time  open 
surface  mixture.  This,  of  course,  quite  does  away  with  the  idea 
that  the  presence  of  soluble  salts  in  Trinidad  asphalt  has  any- 
thing to  do  with  its  disintegration  when  exposed  in  the  refined 
condition  to  the  continued  action  of  water.  As  a  matter  of  fact, 
the  bitumen  of  Trinidad  asphalt  is  not  in  itself  attacked  by  sea- 
water  under  the  conditions  imposed  by  Messrs.  Whipple  and 
Jackson. 

When  the  material  which  has  become  disintegrated  and  brown 
under  these  tests  is  remelted  the  original  bitumen  is  recovered  in 


468 


THE  MODERN  ASPHALT  PAVEMENT. 


an  unchanged  condition,  both  as  to  consistency  and  softening  point. 
The  action  of  the  water  seems,  therefore,  to  be  in  this  case  caused 
by  its  absorption  by  some  of  the  organic  matter  or  non-bituminous 
matter  which  the  asphalt  contains.  If  the  vegetable  matter  is  so 
sealed  up  in  the  asphalt  or  in  the  surface  mixture  as  to  prevent 
diffusion  no  disintegration  occurs.  As  a  preventive  against  the 
slightest  diffusion  the  presence  of  a  material,  such  as  Portland 
cement,  which  will  combine  with  the  water  is  desirable.1 

That  asphalt  surfaces  can  be  constructed  from  any  asphalt 
so  that  they  will  not  be  attacked  by  water  has  been  conclusively 
proved  within  the  last  few  years.  In  the  same  way  it  has  been 
equally  conclusively  proved  that  all  asphalts,  under  certain  con- 
ditions, are  more  or  less  attacked  by  water. 

That  a  distinct  advance  has  been  made  along  this  line  can  be 
seen  by  comparing  the  amount  of  water  absorbed  by  the  surfaces 
of  1894  as  compared  with  those  of  ten  years  later,  as  shown  in  the 
following  table: 

ABSORPTION    OF   WATER    BY   CYLINDERS    OF   ASPHALT   SUR- 
FACE.    IN    POUNDS    PER    SQUARE    YARD. 


Washington,  1893. 

Standard  Mixture,  1904. 

Trinidad. 

Bermudez. 

Trinidad. 

Bermudez. 

7  days.  . 
28    "   !! 

.314 
.434 
.502 

.063 
.194 
.306 

.080 
.093 
.107 

.094 
.093 
.104 

The  conditions  to  which  asphalt  surface  mixtures  are  sub- 
jected  in  the  street  and  in  the  laboratory  bear  no  relation  to  one 
another.  In  the  ordinary  laboratory  tests  surface  mixtures  are 
submitted  to  the  continued  action  of  water,  except  when  bur- 
nished  from  time  to  time  with  a  burnishing-tool  for  experimental 
purposes,  and  receive  no  compaction  as  does  the  street  surface 
from  the  traffic  which  it  receives.  In  the  street  an  asphalt  sur- 


1  See  page  27:  P.  C.  as  a  Filler. 


ACTION  OF  WATER  ON   ASPHALT  PAVEMENTS.  469 

face  is  never  subjected,  at  least  in  well  constructed  pavements, 
to  the  continued  action  of  water.  The  conditions  are,  there- 
fore, in  this  respect  very  different  from  any  which  are  found  in 
laboratory  experiments.  The  conclusion  must,  therefore,  be 
drawn  that  we  must  be  guided  in  forming  an  opinion  in  regard 
to  the  availability  of  any  material  by  the  results  obtained  in  prac- 
tice and  not  by  theoretical  deductions  from  laboratory  experi- 
ments. The  asphalt  surface  laid  on  Fifth  Avenue,  New  York, 
a  thoroughly  well-constructed  surface,  if  the  presence  of  an  open 
binder  is  barred,  has  been  practically  unacted  upon  by  water, 
although  made  of  Trinidad  asphalt,  in  the  ten  years  of  its  exist- 
ence, since  no  repairs  of  any  amount  have  been  made  to  the  pave- 
ment due  to  deterioration  of  the  mixture.  No  doubt  a  very 
Email  amount  of  deterioration  may  be  detected  in  the  gutters 
along  the  curb,  but  this  would  have  been  the  same  in  the  case  of 
other  asphalts  as  in  the  Trinidad  mixture  and  does  not  reach  an 
extent  to  demand  consideration. 

In  this  connection  it  is  of  interest  to  call  attention  to  the  fact 
that  a  process  has  been  patented  for  washing  crude  Trinidad 
asphalt  for  the  removal  of  soluble  salts  before  it  is  refined,  and 
that  it  is  true  that  material  thus  treated  withstands  laboratory 
tests  to  a  somewhat  better  degree  than  the  untreated  material 
when  exposed  to  the  action  of  water  in  the  refined  condition,  but 
the  behavior  of  the  surface  mixture  is  not  improved  by  it  to  any 
appreciable  extent,  and  the  process  must,  therefore,  be  regarded 
as  involving  an  additional  expense  with  no  compensating  return. 

In  conclusion  the  author  may  state  with  the  utmost  conviction 
that  no  Trinidad  asphalt  pavements  which  have  been  laid  under 
his  direction  in  the  last  ten  years  have  suffered  from  the  attack 
of  water  when  a  proper  form  of  construction  has  been  employed. 
All  attempts  which  have  been  and  are  now  being  made  to  prove 
the  contrary  are  based  purely  upon  personal  and  political  attempts 
to  disparage  the  nature  of  the  material. 

SUMMARY. 

An  endeavor  is  made  in  the  preceding  chapter  to  show  that 
the  conclusions  derived  from  laboratory  experiments  and  from 


470  THE    MODERN    ASPHALT    PAVEMENT. 

the  results  of  poor  workmanship,  as  regards  the  action  of  water 
on  asphalt  surfaces,  are  not  practical,  but  merely  theoretical.  It 
is  shown  that  with  requisite  skill,  surface  mixture  can  be  made 
from  those  asphalts  which  are  themselves  attacked  by  water  in 
the  refined  state  in  the  laboratory  which  will  not  be  at  all 
attacked  by  water  either  in  the  laboratory  or  on  the  street. 
Statements  to  the  contrary  generally  originate  in  a  desire  to  damage 
the  reputation  of  a  material  for  reasons  arising  in  business  rivalry. 


PART  VIII. 

CAUSES  OF  THE  DEFECTS  IN  AND  THE  DETERIO- 
RATION OF  ASPHALT  SURFACES. 


CHAPTER  XXV. 
DEFECTS  IN  AND  DETERIORATION  OF  ASPHALT  PAVEMENTS. 

ASPHALT  surfaces,  like  all  pavements,  necessarily  deteriorate 
with  age  even  when  they  are  originally  of  the  most  acceptable 
form  of  construction.  When  they  are  not  well  constructed  they 
deteriorate  very  rapidly. 

Defects  in  asphalt  surfaces  are  more  apparent  than  in  any 
other  form  of  pavement,  since  it  is  a  continuous,  smooth  surface 
without  joints.  The  eye,  as  well  as  the  effect  of  any  irregularity 
upon  the  vehicle  passing  over  it,  reveals  them  at  once,  where  the 
difference  between  a  perfect  and  worn  stone  or  brick  surface  is 
not  as  noticeable. 

The  proper  method  of  construction  of  an  asphalt  pavement 
and  the  characteristics  of  a  desirable  asphalt  surface  mixture 
have  already  been  elaborated.  At  this  point  it  seems  appropriate 
to  sum  up  the  causes  of  the  deterioration  in  such  surfaces  which 
are  due  to  defects  in  construction  or  environment  and  to  follow 
this  with  an  examination  of  the  causes  of  legitimate  wear. 

Deterioration  of  or  defects  in  asphalt  pavements  are  attributed 
to  three  principal  causes  and  many  minor  ones: 

471 


472  THE  MODERN  ASPHALT  PAVEMENT. 

1.  Defects  in  construction  due  to 

A.  Improper  specifications  or  form  of  construction. 

B.  Lack  of  lateral  support. 

C.  Inferiority  of  sand,  in  the  character  of  the  filler  or  lack 

of  a  sufficient  amount  of  it. 

D.  Inferiority  in  the  asphalt  or  lack  of  intelligence  in  its  use. 

E.  Careless  workmanship  and  ignorance. 

2.  Unfavorable  environment. 

A.  Climate. 

B.  Lack  of  cleanliness  and  general  neglect. 

C.  Action  of  water,  of  illuminating-gas,  or  of  gas  and  water 

combined. 

D.  Flushing  with  water  under  pressure. 

E.  Constant  opening  of  the  surface  for  underground  work. 

3.  Age. 

A.  Natural  wear. 

B.  Neglect  of  maintenance. 

Improper  Specifications. — It  often  happens  that  from  motives 
of  economy  specifications  provide  for  a  form  of  construction  of 
asphalt  pavements  which  is  deficient  in  one  or  more  respects  from 
what  is  necessary  to  enable  them  to  meet  the  conditions  to  which 
they  are  to  be  exposed. 

Particular  attention  has  already  been  drawn  to  faulty  pro- 
visions for  a  suitable  foundation  and  for  proper  drainage.  Itishardly 
necessary  to  recur  again  to  this  matter  here  except  to  emphasize 
the  fact  that  without  a  rigid  foundation  and  pro  per  protection  of  the 
surface  mixture  from  water  reaching  it  from  the  bottom,  or  standing 
on  or  flowing  constantly  over  the  top,  an  asphalt  pavement  in 
every  other  way  of  the  highest  type  of  construction  cannot  have 
a  long  life,  at  least  without  extensive  maintenance. 

Specifications  are  also  at  fault  in  regard  to  the  depth  of  the 
binder  course  required.  An  inch  of  binder  made  of  inch  stone 
cannot,  in  the  writer's  opinion,  form  a  sufficient  bond  to  keep  it 
from  going  to  pieces  under  constant  traffic,  especially  if  it  is  sup- 
ported by  only  a  weak  base.  It  is  probable  that  on  the  heaviest 
travelled  streets  in  our  large  cities  an  open  binder  course  is  an 
unsatisfactory  form  of  construction.  In  summer  when  the  surface 
is  soft  the  binder  is  crushed  under  the  weight  of  trucks  with  too 


DEFECTS  ^AND  DETERIORATION.  473 

narrow  tires,  carrying  loads  of  as  much  as  seven  tons,  particularly 
when  the  binder  stone  is  not  hard.  The  binder  in  such  cases  should 
be  replaced  by  a  denser  mixture,  one  in  which  the  voids  in  the 
stone  are  filled  by  a  bituminous  mortar,  in  fact,  the  regular  asphaltic 
surface  mixture.  Such  an  asphaltic  concrete  supports  the  surface, 
most  satisfactorily  distributes  the  load  over  the  base,  and  is  of 
great  advantage  when  placed  over  a  base  subject  to  vibration, 
such  as  stone  blocks  which  have  been  reset,  or  laterally  against  a 
vibrating  rail.  Specifications  for  such  a  course  have  already 
been  given. 

The  thickness  of  surface  specified  is  less  often  at  fault.  If 
properly  supported,  an  inch  and  a  half  of  surface  made  of  desirable 
constituents  has  satisfactorily  carried  heavy  traffic.  A  greater 
thickness  may  often  be  preferable  for  business  streets,  but  the 
greater  the  thickness  the  greater  the  difficulty  hi  raking  out  the 
hot  mixture  evenly  and  obtaining  uniform  compaction  and  the 
greater  its  liability  to  displacement  with  the  formation  of  waves  or 
inequalities  hi  the  surface. 

A  very  frequent  fault  in  specifications  for  asphalt  pavements 
is  that  it  is  provided  that  the  street  should  be  constructed  without 
sufficient  crown.  The  only  objection  that  can  be  raised  against  a 
high  crown  is  that  the  pavement  is  slippery  on  the  quarters,  but 
this  is  a  very  small  objection  compared  to  the  fact  that  flat  streets 
are  unsightly  because  it  is  impossible  to  so  grade  them  as  to  throw 
off  all  the  water  and  because  where  water  stands  in  this  way  it 
cannot  but  have  an  undesirable  effect  upon  the  surface.  The 
height  of  a  crown  which  a  pavement  should  have  has  already  been 
considered.1  It  may  be  added  that  defects  due  to  lack  of  crown 
are  more  emphasized  in  careless  work  than  when  the  pavement  is 
laid  with  skilled  labor  and  supervision. 

Lack  of  Lateral  Support. — Attention  has  been  called  to  the  fact 
that  a  sufficient  lateral  support,  free  from  vibration,  is  as  essential 
as  a  rigid  foundation.  An  aaphaltic  surface  cannot  be  expected  not 
to  deteriorate  against  a  rail  which  vibrates  or  against  a  header 
which  is  not  rigid,  where  the  asphalt  joins  some  other  form  of 
roadway. 

1  See  page  451. 


474  THE  MODERN  ASPHALT  PAVEMENT. 

Proper  provision  for  avoiding  deterioration  from  these  causes 
is  rarely  made  and  should  receive  more  attention.  Along  a  rail 
which  shows  the  least  tendency  to  vibration,  paving  brick  in  three 
or  four  rows,  all  laid  as  stretchers  with  broken  joints  in  Portland- 
cement  mortar,  experience  has  shown  is  by  far  the  most  advanta- 
geous form  of  construction,  or,  if  the  asphalt  surface  must  be  car- 
ried to  the  rail,  it  should  be  supported  on  an  asphalt  concrete  and 
not  a  binder. 

Inferiority  of  Available  Sand. — The  important  role  which  sand 
plays  in  the  construction  of  an  asphalt  surface  and  the  great  varia- 
tions which  are  met  with  in  the  character  of  this  material  have  been 
made  plain  in  preceding  pages.  It  is  evident  that  the  sands 
available  in  one  city  may  be  far  inferior  to  those  found  in  another, 
but  this  demands  only  the  more  care  in  selecting  the  best  and 
using  them  with  the  greatest  skill.  In  two  western  cities  it  is  only 
after  seventeen  years'  experience  and  search  for  sand  that  the  proper 
supply  has  been  found.  The  great  improvement  brought  about 
in  the  character  of  the  surface  mixtures  now  laid  in  these  cities  by 
the  use  of  the  sand  finally  selected  is  most  evident  and  satisfactory. 
The  result  points  out  the  great  advantage  derived  from  a  thorough 
knowledge  of  the  characteristics  of  various  sands  and  by  having  in 
charge  of  securing  supplies  superintendents  who  are  thoroughly 
acquainted  with  the  subject.  Where  the  superintendents  are 
incompetent  and  do  not  pay  sufficient  attention  to  their  sand,  the 
surface  mixtures  which  they  produce  are  inferior.  This  is  illus- 
trated by  the  mixtures  laid  by  six  companies  in  the  city  of  New 
York  in  1904,  the  grading  of  which  is  given  on  the  following  page 
in  comparison  with  that  produced  under  the  author's  supervision. 

It  will  be  noted  in  the  table  that  the  mixture  turned  out 
under  the  author's  supervision  in  1904  is  not  up  to  the  stand- 
ard. This  is  due  to  the  fact  that  -the  available  sand  supply  in 
that  year  was  unsatisfactory.  The  other  mixtures  are,  however, 
much  more  unsatisfactory,  and,  although  they  contain  in  all 
cases  a  sufficient  amount  of  bitumen,  they  are  very  deficient  in 
sand  grains  passing  the  100-  and  80-mesh  sieves  and  generally 
contain  far  too  much  coarse  material  of  10-,  20-,  and  30-mesh 
size.  Such  mixtures,  on  this  account,  cannot  result  in  a  sur- 


DEFECTS  AND  DETERIORATION. 


475 


AVERAGE  COMPOSITION  OF  MIXTURES  PRODUCED  IN  NEW 
YORK  CITY  IN  1904  WITHOUT  PROPER  SUPERVISION  OF 
THE  GRADING. 


Com- 
pany 

Bitu- 

Passing! 

flesh. 

Re- 
tained 

PNoy 

men. 

200 

100 

80 

50 

40 

30 

20 

10 

on  10. 

1 

11  o% 

9  0 

3 

7 

17 

20 

13 

12 

8 

2  
3  
4  

11.3 
10.4 
11.8 

10.7 
9.6 
12.2 

5 
5 

8 

4 
7 
6 

18 
18 
20 

11 
14 
12 

11 
13 
14 

14 
12 
11 

13 
10 
5 

2 

1 

5  

10.7 

6.3 

5 

5 

24 

18 

13 

10 

7 

1 

6 

10  8 

8  2 

4 

3 

15 

12 

15 

11 

13 

8 

7l  .... 

10.9 

14.1 

11 

10 

28 

13 

7 

4 

2 

1  Author's  mixture,  1904. 

face  which  will  be  impervious  to  water.  It  will  also  be  noted 
that  the  percentage  of  200-mesh  material  is  lower  than  in 
that  which  the  author  supervises,  although  in  two  instances  it 
is  above  10  per  cent,  in  two  others  over  9  per  cent.  It  must 
be  borne  in  mind  in  this  connection  that  the  sand  in  use  contains 
a  very  considerable  percentage  of  200-mesh  material,  often  6  to 
9  per  cent.  This  material  is  largely  sand  and  does  not  act  as  a 
filler,  so  that  the  deficiency  in  the  above  mixtures  does  not  seem 
as  large  as  it  really  is,  but  they  are  all  of  them  actually  deficient 
in  filler.  In  the  case  of  companies  5  and  6  the  deficiency  is  very 
large,  and  these  mixtures  may  be  pronounced  very  inferior  on 
this  account  and  because  this  deficiency  is  accompanied  by  a 
similar  one  in  fine  sand  and  by  the  presence  of  a  very  large  amount 
of  coarse  material. 

In  other  cities  mixtures  have  been  laid  which  show  even  greater 
deficiencies,  and  illustrate  very  well  the  inferior  character  of  the 
material  which  is  turned  out  without  a  thorough  understanding 
of  the  principles  underlying  the  production  of  a  standard  surface 
mixture,  and  without  proper  laboratory  control.  Had  the  latter 
been  exercised,  the  defects  in  these  mixtures  would  have  become 
apparent  before  the  material  was  laid.  See  table  on  page  476. 

More  gross  defects  in  pavements  are  due  to  the  improper  use 
of  sand  than  to  any  other  causes  except  too  hard  bitumen  or  weak 
foundation. 


476 


THE  MODERN  ASPHALT  PAVEMENT. 


City. 

Bit- 
umen. 

Passing  Mesh. 

Is 

1§ 

16 
1 

2 

200 

100 

80 

50 

40 

30 

20 

10 

Buffalo  N.  Y  

9.2% 
10.6 
8.8 
11.3 
9.9 
9.9 
9.3 
10.6 
9.9 
11.1 
8.7 
9.5 
9.0 
12.7 
9.8 

4.8 
8.4 
16.2 
6.7 
4.1 
9.1 
7.7 
6.4 
12.1 
4.9 
8.3 
11.5 
5.0 
5.3 
5.2 

12 
4 
16 
4 
4 
5 
3 
6 
18 
10 
3 
4 
11 
8 
10 

19 
8 
30 
6 
27 
12 
8 
7 
30 
14 
4 
5 
12 
5 
14 

53 
31 
22 
45 
42 
44 
45 
35 
28 
33 
32 
32 
27 
53 
35 

2 
5 
2 
15 
5 
10 
11 
15 
2 
10 
26 
23 
15 
8 
14 

0 
3 
2 
9 
4 
5 
6 
9 
0 
11 
12 
11 
12 
4 
6 

0 
5 
1 
1 
2 
3 
5 
5 
0 
2 
4 
3 
5 
2 
4 

0 
9 
2 
2 
1 
2 
5 
6 
0 
2 
2 
1 
4 
2 
2 

it           tt 

Chicago,  111  

it         ft 

tt         (t 

Cedar  Rapids,  Iowa..  . 
Erie  Pa  

Long  Island  City,  N.Y. 
Louisville  Ky 

Newark   N   J. 

New  Orleans  La..  .  . 

tt          a         tt 

Omaha  Neb   

Pittsburg,  Pa  

Toronto,  Ont  

It  may  happen,  of  course,  that  in  some  places  the  highest  grade 
of  asphalt-surface  cannot  be  laid  with  the  available  sand  supplies 
and  that  their  lasting  or  wearing  properties  in  such  cities  must, 
therefore,  be  inferior  to  those  which  can  be  laid  in  others  with 
more  suitable  sand. 

Character  of  the  Filler. — As  has  been  shown  1  the  character 
of  the  filler  in  use  in  asphalt-surface  mixtures  is  very  variable.  If 
it  is  coarse  and  used  in  insufficient  amount  the  result  will  be  a 
decidedly  inferior  mixture.  As  an  example  of  this,  certain  streets 
are  known  to  the  author,  which  were  laid  in  the  downtown  sec- 
tion of  New  York  in  1895,  with  an  asphalt  surface  mixture  con- 
taining no  filler.  These  streets  rapidly  lost  their  shape  through 
displacement  of  the  surface  or  lack  of  stability  in  the  mixture, 
and  they  have  long  since  been  resurfaced. 

It  can  be  seen,  therefore,  that  deterioration  of  asphalt  pave- 
ments may  at  times  be  attributed  to  the  lack  of  filler,  to  its  poor 
character  or  to  its  unintelligent  use. 

On  street  surfaces  which  are  to  be  subjected  to  the  heaviest 


1  See  page  89. 


DEFECTS  AND  DETERIORATION.  477 

travel  the  use  of  Portland  cement  as  a  filler  has  been  found  to 
well  repay  the  extra  expense  incurred. 

Inferiority  in  the  Asphalt  or  Lack  of  Intelligence  in  its 
Use. — Defects  due  to  the  character  of  the  asphalt  hi  use  and 
lack  of  intelligence  in  handling  it  are  and  have  been  the  most 
frequent  in  pavements  laid  by  inexperienced  or  unintelligent 
persons.  By  a  proper  combination  of  different  najtive  bitumens 
of  different  properties  an  asphalt  cement  can  be  made  hi  which 
more  or  less  of  any  available  kind  may  form  a  part,  but  certain 
bitumens  require  much  more  skill  in  handling,  while  others  will 
stand  much  greater  abuse.  Trinidad  lake  asphalt  has  been  shown 
to  be  of  the  latter  class,  while  others,  either  deficient  in  hydro- 
carbons of  the  malthene  group,  or  containing  light  oils  volatile 
at  high  temperatures  or  unsaturated  hydrocarbons  which  readily 
become  altered  in  their  state  of  molecular  aggregation  and  con- 
sequently in  their  consistency,  are  of  the  class  which  require  skill 
and  care  in  their  manipulation.  Others  again  necessitate  the 
use  of  particular  fluxing  agents  and  result  in  comparative  failures 
when  improper  ones  are  used.  These  differences  have  been  taken 
up  in  the  description  of  the  properties  of  the  several  native  bitu- 
mens. 

Asphalt  cements  made  in  this  way  with  a  flux  which  is  unsuit- 
able for  the  purpose  may  thus  be  the  cause  of  failure  or  deteriora- 
tion. Such  a  cement  may  contain  an  excess  of  paraffine  scale, 
of  light  oils,  of  cracked  products,  or  of  unsaturated  hydrocar- 
bons, which  are  rapidly  converted  to  pitch  on  heating.  Defects 
in  asphalt  surfaces  have  been  due  frequently  to  such  reasons  in 
the  past.  They  are  not  as  frequent  to-day,  but  public  officials 
cannot  be  too  careful  in  determining  the  quality  of  the  flux  hi 
use  in  preparing  the  asphalt  cement  with  which  a  surface  for 
which  they  are  responsible  is  laid.  Large  numbers  of  Bermudez 
asphalt  pavements  laid  between  1894  and  1900  were  failures 
because  the  asphalt  cement  of  which  they  were  made  was  not 
handled  with  skill. 

Careless  Workmanship. — Poor  workmanship  may  be  due  to 
either  ignorance  or  intention,  and  unfortunately  it  is  too  often 
due  to  both  combined.  The  careless  and  irresponsible  contractor 


478  THE  MODERN  ASPHALT  PAVEMENT. 

* 

who  looks  to  immediate  profits,  who  has  little  experience  in  the 
cost  of  maintenance  of  pavements,  who  does  not  set  aside  a  cer- 
tain amount  of  money  for  this  purpose  or  consider  it  in  his  bid 
for  construction,  is  doing  more  to  discredit  asphalt  pavements 
to-day  than  any  inherent  defects  in  the  pavement^  except  per- 
haps the  public  officials  who  will  not  maintain  their  asphalt  pave- 
ments after  the  expiration  of  the  guarantee  period. 

Aside  from  the  defects  due  to  the  nature  ol  the  asphalt,  to 
the  use  of  improper  sand  and  the  careless  regulation  of  the  mineral 
aggregate,  others  are  attributable  to  asphalt  cement  made,  as 
has  been  shown,  with  an  unsatisfactory  flux,  or  to  the  fact  that 
it  is  too  hard  or  too  soft,  irregular  in  amount  or  hardened,  burned 
as  the  saying  is,  by  too  hot  sand.  All  lack  of  attention  to  pre- 
cautions for  avoiding  such  defects,  which  are  known  to  be  fatal 
to  the  production  of  the  best  surface  mixture,  may  be  set  down, 
largely,  to  carelessness  as  well  as  ignorance. 

Ignorance  or  lack  of  technical  knowledge  on  the  part  of  the 
contractor  can  be  readily  learned  by  inquiry  as  to  whether  the 
requisite  technical  supervision  is  exercised  over  his  work  by  labora- 
tory methods.  A  high-grade  surface,  it  has  been  shown,  cannot 
be  laid  without  such  a  supervision  of  all  the  elements  entering 
into  its  construction. 

Intentional  neglect  of  the  proper  construction  from  motives 
of  economy  can  be  detected  by  public  officials  if  they  are  suffi- 
ciently acquainted  with  the  technology  of  the  industry.  Unfor- 
tunately City  Engineers  are  usually  themselves  insufficiently 
informed  to  do  so,  and  it  is  for  the  purpose  of  instructing  them 
that  this  book  has  been  written.  They  must,  as  a  rule,  depute 
any  inspection  to  subordinates,  who  are  even  less  well  informed, 
who  quibble  over  small  details  and  miss  the  important  points, 
or  to  experts,  men  of  no  wide  practical  experience  but  rather 
theorists,  with  one  theory  one  year,  another  the  next,  abandoning 
an  old  one  for  the  novelty  of  the  new,  but  not  founding  any  of 
them  on  more  than  closet  work  and  experiment,  and  failing  to 
look  back  and  draw  conclusions  of  weight  from  practical  results. 

The  asphalt  surfaces  which  are  laid  to-day  on  a  rational  basis, 
under  the  writer's  supervision,  are  built  on  no  theory  but  by  deter- 


DEFECTS  AND  DETERIORATION.  479 

mining  from  a  study  of  the  composition  of  actual  surfaces  which 
have  given  the  greatest  satisfaction  what  a  desirable  form  of  con- 
struction is.  The  manner  of  working  out  this  problem  has  been 
elaborated  in  previous  pages. 

Public  officials  are  advised  in  determining  the  character  of 
the  work  which  is  being  done  by  any  contractor  who  employs 
no  scientific  supervision  of  his  process  to  note: 

The  number  of  barrels  of  cement  and  the  amount  of  sand  and 
stone  used  in  a  definite  area  of  base. 

The  consistency  of  the  asphaltic  cement  and  its  regularity, 
together  with  the  character  of  the  flux  used  in  its  preparation. 

The  character  of  the  sand  and  its  capacity  for  carrying 
bitumen  and  a  proper  amount  of  filler. 

The  grading  of  the  mineral  aggregate. 

The  regulation  of  the  amount  of  bitumen  in  the  surface 
mixture  by  means  of  the  pat  paper  test. 

The  temperature  of  the  materials. 

The  skill  in  handling  the  materials  at  the  plant  and  on  the 
street. 

The  Manner  in  Which  Defects  in  Asphalt  Surfaces  Due  to 
Faulty  Construction  are  Manifested. — Defects  in  asphalt  pave- 
ments due  to  the  faulty  methods  of  construction  which  have 
been  described,  are  manifested  in  several  ways. 

The  surface  cracks,  but  does  not  disintegrate. 

The  surface  cracks  when  the  lateral  support  is  weak  and  then 
goes  to  pieces  under  traffic. 

The  surface  disintegrates  in  various  parts  of  the  roadway, 
forming  depressions  or  holes  extending  to  the  base. 

The  surface,  when  wet,  scales  off  in  large  thin  patches. 

The  surface  is  displaced  upon  the  base  becoming  wavy,  high 
at  one  spot  and  below  grade  at  another. 

The  surface  is  raised  into  waves  by  expansion  of  the  hydraulic 
cement  in  the  concrete  base. 

Cracking  in  asphalt  surfaces  have  been  found  to  be  due  to 
many  different  causes: 

Induced  by   cracks    in  the  hydraulic    concrete    forming  the 


480  THE  MODERN  ASPHALT  PAVEMENT. 

Produced  by  too  hard  a  bitumen  in  the  surface  mixture,  or 
by  one  which  is  not  sufficiently  ductile  at  low  temperatures. 

Produced  by  too  small  a  percentage  of  bitumen  in  the  surface. 

Produced  by  the  use  of  an  unsuitable  bitumen. 

Produced  by  an  unsuitable  mineral  aggregate. 

Produced  by  lack  of  compression. 

Produced  by  lack  of  traffic. 

Produced  by  sudden  changes  in  temperature. 

Produced  by  vibration  of  rails,  manholes  and  valve-boxes. 

Cracking  of  Asphalt  Surfaces. — Cracks  in  the  hydraulic  con- 
crete base  are  at  times  reproduced  in  asphalt  surfaces,  even  when 
the  latter  are  of  the  best  quality.  The  causes  of  cracks  in  base  of 
this  description  must  be  referred  to  defects  in  the  cement  of  which 
it  is  made,  some  of  them  expanding  or  contracting  for  some  years 
after  their  use.  Cracks  due  to  this  cause  may  be  directly  across 
the  street  or  run  in  zig-zag  directions  along  the  crown  and  else- 
where, as  shown  in  the  illustration,  Fig.  1,  where  cracks  in  the 
surface  have  been  cut  out  to  show  those  in  the  base.  This  form  of 
cracking  occurs  both  with  natural  and  Portland  cement,  and  with 
the  very  best  surface  mixtures  under  traffic,  as  well  as  with  inferior 
ones  under  no  traffic. 

If  the  cracked  portions  are  renewed  after  the  cement  has  attained 
volume  constancy  with  age  and  the  surface  repaved,  the  cracks 
do  not  return.  They  are  not  a  common  form  of  defect  in  an 
asphalt  surface. 

Cracks  of  the  second  description,  due  to  the  use  of  asphalt 
cement  which  is  too  hard  or  which  has  become  hardened  by  being 
mixed  with  too  hot  sand,  or  to  this  cause  combined  with  others, 
are  the  form  which  is  most  commonly  met  with.  They  are  fre- 
quent in  the  hard  Bermudez  pavements  laid  in  the  Central  States 
in  1898  and  1899,  where  the  work  was  done  according  to  a  formula 
suitable  for  the  materials  available  in  1893,  but  which  with  changed 
conditions  resulted  in  later  years  in  an  asphalt  cement  of  great 
hardness.  Intelligence  or  proper  supervision  would  have  detected 
the  unsuitable  consistency  of  the  cement.  The  results  indicate 
the  danger  of  following  a  blind  formula. 

Such  cracks  are  of  course  due  to  the  fact  that  the  hard  asphalt 


DEFECTS  AND  DETERIORATION. 


481 


is  too  brittle  at  low  temperatures  to  yield  to  the  contraction  of 
the  surface  It  fractures  under  the  tensile  stress  imposed  upon  it. 

An  actual  measurement  of  the  contraction  of  an  asphalt 
surface  made  by  Mr.  E.  C.  Wallace,  formerly  Chemist  of  the 
Warren-Scharf  Asphalt  Paving  Company,  outside  the  window 
of  his  laboratory  during  cold  winter  weather,  has  shown  that  above 
32°  F.  it  is  less  than  the  average  contraction  of  steel,  and  below 
freezing  greater.  This  contraction  is  about  that  of  quartz,  and  as 
quartz  or  similar  mineral  matter  forms  nearly  90  per  cent  of  the 
mixture  such  a  contraction  would  be  expected. 

Determinations  of  the  coefficient  of  expansion  of  various 
materials  have  been  collected  in  the  following  tables  from  the 
literature  of  the  subject,  and  a  few  determinations  made  by  the 
writer  are  given  for  that  of  residuum  and  asphalt  cements. 

COEFFICIENTS  OF  LINEAR  EXPANSION   FOR   1°  C. 


Substance. 

Temperature. 

Coefficient. 

Authority. 

Quartz,  mean  

0°-100°  C. 

1,000,010  67 

Benoit 

~~  «            <  < 

0°-100°  C. 

,000,011.80 

Pulfrich 

Steel 

0°-100°  C 

000010  9 

Benoit 

Petroleum  26°  B  

0°-100°  C. 

000095 

Sharpless 

<  «               « 

100°-101°  C. 

,000,147 

Paraffine,  hard  

0°-  16°  C. 

,000,106.6 

Rodwell 

«            i< 

16°-  38°  C 

000  130  3 

<  < 

Beeswax 

10°-  26°  C 

000  230 

KODD 

<  < 

26°-  31°  C. 

,000312 

ixupp 

Eastern  petroleum: 
Residuum,  21°  B.  .  . 

14°-  27°  C. 

,000,989 

Richardson 

n                a 

23°-  38°  C 

000  838  9 

tt 

Bermudez  asphalt  cement  

100  asphalt,  20  residuum.  .  . 
«         «<         «<            it 

6°-  20°  C. 
20°-  45°  C. 

,000,544 
,000,302 

tt 
tt 

The  coefficient  of  expansion  of  petroleum  residuum  does 
not,  like  that  of  most  oils,  increase  with  rise  in  temperature,  prob- 
ably due  to  the  presence  of  paraffine,  which  solidifies  at  low  tempera- 
tures and  contracts  rapidly.  The  bitumen  of  asphalt  and  asphalt 
cements  contracts  or  expands  in  the  same  way.  These  results  at 
first  seemed  rather  startling,  but  reference  to  the  literature  of 
the  subject  confirms  them.  A  paper  by  Holde  in  Mittheilungen 
der  Konig,  Technische  Versuchsstation,  1893,  45-68,  shows  that: 


482  THE  MODERN  ASPHALT  PAVEMENT. 

"  The  heavy  viscous  products  of  distillation  or  residues  from 
crude  petroleum  of  different  origin,  possessing  a  specific  gravity 
of  at  least  0.908,  do  not  sho.w  any  marked  difference  in  their  expan- 
sions between  +20°  C.  and  78°  C.  Their  coefficient  of  expansion 
varies  from  0.00070  to  0.00072.  Those  oils  holding  solid  paraffine 
suspended  at  temperatures  below  +  20°  C.  (as  German  oils)  have 
a  higher  coefficient  of  expansion  between  18°  C.  and  20°  C.,  viz. 
0.00075  and  0.00081,  owing  to  the  melting  of  the  solid  particles. 

"  The  heavy  liquid  products  of  distillation,  of  specific  gravities 
below  0.905,  at  + 15°  C.  possess  a  higher  coefficient  of  expansion 
between  20°  C.  and  78°  C.,  viz.  0.00072  to  0.00076.  The  American 
and  Scotch  oils  belong  to  this  class. 

"As  to  the  completely  fluid  lubricating  oils,  their  coefficients 
of  expansion  rise  gradually  in  proportion  to  the  increase  of  tempera- 
ture." 

In  an  asphalt  surface  one  thousand  feet  long  between  —  20°  F. 
and  130°  F.,  extremes  of  temperature  that  are  met  with  by  Omaha 
surfaces,  the  contraction  of  the  sand  alone,  forming  90  per  cent 
of  the  pavement,  would  amount  to  from  .902  to  .920  feet,  or  from 
10  to  11  inches.  The  contraction  of  the  bitumen  need  not  be 
considered,  as  this  either  elongates  under  the  stress,  or  fractures. 
As  low  as  26°  F.  the  elongation  of  a  bitumen  of  proper  consistency 
has  been  shown  by  experiments,  to  be  described  later,  to  take 
place  quite  readily.  The  contraction  need  therefore  be  considered 
only  for  the  temperature  between  26°  and  -20°,  46°  F.  or  25°  C. 
For  such  an  interval  it  would  amount  to  about  .29  of  a  foot  per 
1000  feet,  or  about  1  inch  in  a  Fifth  Avenue,  New  York,  block.  It 
is  not  surprising,  therefore,  that  with  a  hard  cement  rupture  of  the 
surface  takes  place,  but  rather  that  it  does  not  always  take  place. 

The  above  conclusions  are  based  entirely  on  theoretical  consider- 
ations. Mr.  S.  Whinery  and  Mr.  E.  C.  Wallace,  of  the  Warren- 
Scharf  Asphalt  Paving  Company,  made  some  actual  determinations 
some  years  ago  of  the  expansion  of  an  asphalt  surface  mixture  on  a 
laboratory  scale.  The  means  of  measurement  were  not  more 
accurate  than  1/1000  inch.  Using  only  those  observations  where 
the  difference  of  temperature  was  20°  F.  or  more,  and  the  expan- 


DEFECTS    AND    DETERIORATION. 


483 


sion  or  contraction,  therefore,  so  considerable  that  it  could  be 
measured  in  this  way  with  a  fair  degree  of  accuracy,  they  arrived 
at  results  which  seem  to  be  worthy  of  some  confidence.  There 
were  four  series  of  these  observations,  and  the  results  are  given 
in  the  following  table. 


COEFFICIENT   OF   EXPANSION   BY   HEAT    OF   SHEET   ASPHALT 

«         PAVEMENT.     FROM  OBSERVATIONS  MADE  BY  LABORATORY 

OF  THE  WARREN-SCHARF  ASPHALT  PAVING   COMPANY. 


Series. 

No.  of  Observa- 
tions Used. 

Mean  Coefficient 
of  Expansion. 

A  . 

13 

0000135 

B  

17 

.0000140 

C    . 

12 

0000139 

D  

9 

0000131 

As  the  coefficient  of  expansion  of  structural  steel  is  about 
.0000065,  it  is  nearly  correct  to  say  that  the  coefficient  of 
expansion  of  asphalt  surface  mixture  as  determined  in  this  way  is 
double  that  of  steel. 

These  results  are  about  half  of  that  which  is  arrived  at  theo- 
retically. What  weight  can  be  given  to  the  results  is  some- 
what doubtful,  but  they  are  quoted  here  for  what  they  are 
worth. 

Cracks  which  are  due  to  the  fact  that  the  mixture  is  deficient 
in  bitumen,  in  consequence  of  which  the  surface  does  not  possess 
sufficient  tensile  strength,  regardless  of  ductility,  at  low  winter 
temperatures,  are  not  as  frequent  as  those  due  to  a  hard  bitumen, 
since  in  such  a  mixture,  disintegration  with  the  formation  of 
holes  takes  place,  as  a  rule,  before  cracking. 

Cracks  may  be  caused  by  the  use  of  an  asphalt  cement  which 
is  unsuitable  for  the  purpose  to  which  it  is  applied.  It  may  be 
too  susceptible  to  temperature  changes,  so  that,  even  if  made  so 
soft  that  the  surface  marks  badly  under  a  summer  sun,  it  may 
be  brittle  at  zero. 


484  THE   MODERN    ASPHALT  PAVEMENT. 

Finally,  an  asphalt  cement  may  so  harden  with  age  that  it 
becomes  brittle  in  the  course  of  a  few  years.  Coal-tar  is  an 
example  of  such  a  material. 

Cracking  may  be  caused  even  with  the  most  satisfactory  asphalt 
cement  by  an  unsuitable  sand  or  mineral  aggregate.  Sands  are 
known  and  have  been  used,  the  surface  of  the  grains  of  which 
are  of  such  a  nature  that  melted  asphalt  cement  will  not  adhere 
to  them  in  sufficient  thickness,  and  the  voids  in  which  are  so  small 
as  to  prevent  the  mixture  from  holding  enough  bitumen  to  give 
the  pavement  ductility.  The  sands  available  in  other  cities, 
without  appreciable  difference  from  those  in  use  elsewhere,  pro- 
duce a  surface  which  never  cracks,  even  under  unfavorable  con- 
ditions and  inferior  workmanship. 

Too  fine  a  mineral  aggregate  may  be  a  disadvantage  on  streets 
of  little  or  no  traffic. 

Lack  of  density  in  the  surface  also  favors  cracking,  whether 
brought  about  by  insufficient  compaction  when  the  surface  is 
laid  or  subsequent  lack  of  traffic. 

Traffic  and  the  lack  of  it  play  a  large  part  in  preventing  or 
causing  the  cracking  of  pavements. 

Traffic  releases  tension  to  a  large  degree  in  a  cold  asphalt  sur- 
face and  assists  elongation  of  the  bitumen,  so  that  heavy-traffic 
streets  do  not  crack  as  readily  as  those  of  light  or  no  traffic,  and 
oftener  crack  only  in  the  gutters,  if  at  all,  while  light-traffic  streets 
crack  entirely  across  the  roadway. 

Suburban  streets,  not  benefited  by  traction,  at  least  in  certain 
cities,  are  much  more  liable  to  crack  than  those  which  have  a 
medium  traffic.  This  is  particularly  well  illustrated  in  a  Canadian 
city  where  surfaces  with  only  8  to  9  per  cent  of  bitumen  are  free 
from  cracks  on  the  downtown  streets  but  are  a  mass  of  cracks 
in  the  suburbs,  the  bitumen  present  not  being  sufficient  to  give 
any  elasticity  unless  the  tension  produced  by  contraction  is 
released  by  traffic. 

Climate,  of  course,  plays  a  large  part  in  deteraiining  the  fre- 
quency of  cracks  in  asphalt  surfaces.  Mixtures  of  almost  identical 
composition  will  fracture  under  the  conditions  met  with  in  one 


DEFECTS    AND   DETERIORATION. 


485 


city  and  not  in  another.  In  those  cities  in  the  Missouri  valley 
where  sudden  changes  in  temperature  reaching  60°  in  a  few  hours, 
from  40°  above  zero  to  20°  below,  cracking  frequently  results, 
where  the  same  changes  occurring  more  slowly  in  more  protected 
locations  do  no  damage. 

Cracking  along  rails  and  around  boxes  and  manholes  is  due 
to  lack  of  support  and  may  occur  with  the  best  mixtures.  The 
causes  have  been  considered  elsewhere. 

In  all  of  the  causes  of  cracking  which  have  been  cited,  except 
the  last,  laboratory  investigations  have  thrown  some  light  on  the 
subject  and  the  results  obtained  are  of  interest. 

Strength  of  Asphalt  Surfaces. — An  asphalt  surface  having  the 
least  ductility  and  tensile  strength  will,  of  course,  rupture  most 
readily  under  the  tensile  stress  produced  by  contraction  due  to 
a  fall  of  temperature.  The  tensile  or  crushing  strength  of  an 
asphalt  surface  is,  of  course,  a  function  of  the  temperature  being 
greater  at  low  than  high  temperature.  Following  are  illustrations: 


FIFTH   AVENUE,   NEW   YORK.      LAID   IN    1897. 


Temperature. 

6°  F. 

38°  F. 

76°  F. 

Pounds  per  square  inch: 
Tensile  strength 

880 

568 

300 

Crushing     '  *       

4862 

2836 

1820 

In  considering  the  subject  of  cracked  pavements  our  interest 
is  entirely  in  the  strength  and  ductility  of  the  surfaces  at  low 
temperatures. 

From  a  great  many  old  surfaces,  some  of  which  had  cracked 
and  some  of  which  were  free  from  them,  briquettes  were  made 
and  broken  at  6°  F.  Averages  of  these  determinations  for  the 
cracked  and  good  surfaces  in  two  cities  are  as  follows: 


486  THE   MODERN    ASPHALT    PAVEMENT. 

TENSILE  STRENGTH  IN  POUNDS  PER  SQUARE  INCH  AT  6°  F. 

No.  1. 

Cracked  pavements 664  (6) 

Good  "  722  (2) 

No.  2. 

Cracked  pavements 497  (2) 

Good  "        614  (6) 

There  is  a  striking  difference  in  the  strength  of  the  cracked 
and  the  good  pavements  in  both  cities  in  favor  of  the  latter. 

It  is  of  interest  in  this  connection  to  know  what  peculiarities 
contribute  to  the  strength  of  asphalt  surfaces.  Experiments  have 
shown  that  the  principal  conditioning  elements  are: 

Asphalt  Cement. 

Character. 

Consistency. 

Amount. 
Filler. 

Amount. 
Sand. 

Grading. 
Density  of  the  surface. 

This  subject  was  looked  into  to  a  considerable  extent  by  the 
writer  in  1894.  Unfortunately  this  work  was  done  with  the 
old  coarse  Washington  surface  mixture.  With  the  modern  well 
graded  New  York  material  more  satisfactory  results  would  now  be 
obtained.  The  experiments  suffice,  however,  to  bring  out  several 
points.  Following  are  the  available  data.  See  table  on  page  487. 

These  results  show  that  the  character  of  the  cementing  material 
has  a  very  decided  influence  on  the  crushing,  and  it  would  also  be 
found  to  be  the  same  on  the  tensile  strength  of  the  surfaces.  This 
subject  was  thoroughly  discussed  by  the  writer  in  a  letter  in  the 
Engineering  News  for  June,  1894,  and  it  need  only  be  said  here 
that  the  strongest  mixture  is  not  the  best,  without  regard  to  the 
nature  of  the  bitumen,  but  that,  with  a  proper  cement,  weakness 


DEFECTS    AND    DETERIORATION. 


487 


EFFECT  OF  THE  CHARACTER   OF   THE   BITUMEN  ON  THE 
CRUSHING  STRENGTH. 

CRUSHING   STRENGTH   OF   MIXTURES  OF  COAL-TAR,   TRINIDAD   LAKE   AND 

LAND,   BERMUDEZ,    AND    PEDERNALES   ASPHALT. 

POUNDS  PER  SQUARE  INCH. 


Mixture. 

Density. 

At  38°  F. 

At  77°  F. 

Coal-tar   15%.  .  .                       

2.16 

3880 

1254 

"         10%  

2.07 

3845 

2655 

Land  pitch  cement   15%  or  10%  bitumen 

2  13 

1813 

761 

Bermudez  cement,  10%  or  10%  bitumen  

2.10 

1955 

635 

Pedernales  asphalt,  10%  or  10%  bitumen 

2  06 

2125 

550 

Lake  pitch  cement,  15%  or  10%  bitumen  

2.14 

1375 

548 

Ten  per  cent  of  dust  and  Washington  sand  in  all  mixtures. 

at  low  temperatures  due  to  ductility  or  elongation  is  preferable 
to  high  strength;  weakness  due  to  lack  of  bitumen,  on  the  contrary, 
is  not. 

EFFECT   OF  THE   CONSISTENCY  OF   ASPHALT   CEMENT   ON 
STRENGTH  OF  SURFACES. 

WASHINGTON  MIXTURE,    1894,   POUNDS   PER  SQUARE  INCH. 


Softness. 

Crushing  Strength. 

Shearing  Strength. 

36°  F. 

77°  F. 

36°  F. 

77°  F. 

Trinidad  cement: 
Normal  consistency.  .  .  . 

1703 
1610 

2416 
3028 

680 
682 

741 
602 

2865 
2005 

3193 
2569 

1425 

1873 

1528 
1876 

Softer  cement  3  Ibs.  more  oil.  . 

Bermudez  cement: 
Normal  consistency  

Softer             "          

These  results  show  that  a  softer  Trinidad  cement  makes  a 
mixture  which  has,  owing  to  its  great  ductility,  a  smaller  crushing 
strength  at  36°  than  the  one  made  with  a  hard  cement;  but  with 
Bermudez  cement  this  is  not  the  case,  as  this  cementing  material 
is  more  easily  affected  by  a  fall  of  temperature. 

With  a  better  sand  grading,  however,  the  above  results  might 
be  somewhat  modified. 


488 


THE    MODERN    ASPHALT    PAVEMENT. 


EFFECT    OF    THE    QUANTITY     OF    ASPHALT    CEMENT    ON 

STRENGTH     OF    SURFACES. 
WASHINGTON   MIXTURE,  1894,  POUNDS    PER   SQUARE   INCH. 


Crushing 

Strength. 

Shearing 

Strength. 

36°  F. 

77°  F. 

36°  F. 

77°  F. 

Trinidad  cement  : 
Normal  15%.  .  . 

1703 

880 

2865 

1425 

More  cement  16  5%. 

2425 

768 

2882 

2378 

Bermudez  cement: 
Normal  10%  

2416 

741 

3193 

1528 

More  cement  11%   

2544 

961 

2511 

1636 

These  results  show  that  an  increase  in  the  amount  of  asphalt 
in  a  mixture,  up  to  a  certain  point,  increases  the  strength  of  a 
Trinidad  mixture  in  all  cases;  but,  as  before,  not  always,  with 
Bermudez  asphalt  due  to  differences  in  the  physical  properties  of 
the  two  bitumens  at  low  temperatures. 

EFFECT    OF    INCREASE    OF    AMOUNT    OF    DUST    IN    SURFACE 

MIXTURES   ON   THEIR  TENSILE  STRENGTH. 

POUNDS  PER  SQUARE  INCH. 


Dust 
per  Cent. 

Trinidad 
at  36°  F. 

Bermudez 
at  36°  F. 

Trinidad 
at  77°  F. 

Bermudez 
at  77°  F. 

7.5 
10.0 
15.0 
20.0 

501 
604 
646 
701 

449 
611 
662 

857 

188 
205 
273 
270 

Ill 

171 
186 
192 

The  addition  of  increased  amounts  of  dust  gives  decided  evi- 
dence of  improvement  of  the  mixture  in  all  cases,  and  shows  the 
necessity  of  using  plenty  of  filler. 

EFFECT  OF  DENSITY  ON  STRENGTH  OF  SURFACES. 


Tensile  Strength  at 

Compaction. 

40°  F.       |        77°  F.       |       90°  F. 

Density. 

Pounds  Per  Square  Inch. 

Least  dense  

463 
646 

152 
273 

101 
166 

2.08 
2.23 

Densest  

DEFJECTS    AND    DETERIORATION. 


489 


The  above  results  show  that  there  can  be  no  doubt  that  the 
densest  mixtures  are  the  strongest,  at  least  with  the  same  mineral 
aggregate  and  a  sufficient  amount  of  bitumen. 

EFFECT  OF  SAND  GRADING  ON  STRENGTH  OF  SURFACES. 
WASHINGTON  AND  NEW  YORK. 


Composition. 

Bitu- 
men. 

Passing. 

200 

100 

80 

50 

40 

30 

20 

10 

New  York.. 
Washington. 

10.6 
10.5 

14.4 
9.7 

11.0 
3.2 

12.0 
5.4 

27.0 
22.3 

11.0 
20.5 

7.0 
13.2 

4.0 
7.8 

3.0 
7.4 

TENSILE  STRENGTH,  POUNDS  PER  SQUARE  INCH. 


At  38°  F. 

At  78°  F. 

New  York  

568  Ibs. 

300  Ibs. 

^r£Lshinfirton 

604    " 

205    " 

The  difference  between  the  fine  and  coarse  mixture  at  36°  F. 
is  slightly  in  favor  of  the  coarse;  at  78°  F.  in  favor  of  the  fine. 

It  must  be  remembered,  however,  that  in  these  tests  there 
are  a  number  of  conditions  beside  the  grading  of  the  sand  that 
enter  into  the  problem,  so  that  final  conclusions  can  hardly  be 
drawn  from  so  few  experiments. 

As  a  whole  the  results  of  these  physical  tests  throw  considerable 
light  on  the  peculiarities  of  mixtures  of  varying  composition  and 
give  us  some  information  as  to  why  some  crack  and  others  do  not. 

The  possibility  of  cracking  in  asphalt  surfaces  are  seen  to 
be  large,  and  it  is  remarkable  how  well  they  have  been  overcome 
by  intelligent  study  of  the  conditions  that  are  to  be  met.  There 
is  still  much  to  be  learned  in  this  direction.  It  is  impossible,  as 
yet,  to  say  why  cracking  has  never  occurred  in  pavements,  even 
when  not  laid  with  the  greatest  care,  in  one  city,  while  they  are 
of  general  occurrence  in  another  where  the  greatest  care  is  exer- 
cised. It  must,  of  course,  be  due  to  peculiarities  in  the  surface 
of  the  grains  of  the  sands  in  use,  and  the  relative  degree  of 
adhesion  of  asphalt  to  them. 


490  THE    MODERN    ASPHALT   PAVEMENT. 

Cracks  are  never  known  to  heal.  Experiments  have  shown 
that  an  asphalt  contracts  longitudinally;  but  expands  vertically, 
BO  that  cracks  once  formed  increase  in  width  every  winter,  not 
only  for  this  reason  but  because  they  become  filled  with  dirt. 

Cracks  may  be  merely  unsightly  or  they  may  be  the  essential 
cause  of  subsequent  disintegration. 

Asphalt  surfaces  on  suburban  streets  in  some  climates  crack 
to  a  marked  degree  after  about  three  years  service ;  but  if  the  sur- 
face mixture  is  a  good  one,  no  disintegration  follows  and  the  pave- 
ment continues  to  be  satisfactory  in  every  other  respect  for  as 
long  a  period  as  if  no  cracks  existed.  If  disintegration  takes 
place  in  such  cases  it  is  due  to  inferiority  hi  the  character  of  the 
mixture.  There  need  be  no  alarm  if  no  disintegration  sets  in. 
If  local  prejudice  against  a  very  soft  surface  which  marks  excessively 
when  first  laid  does  not  exist,  cracks  may  be  largely  avoided  by 
using  a  very  soft  asphalt  cement  in  the  surface.  In  a  north- 
western city,  where  no  asphalt  surface  had  ever  been  laid  on  a 
residence  street  without  cracks  appearing  hi  a  few  years,  this  was 
avoided  in  some  laid  by  the  writer  by  using  a  cement  of  90  to 
100  penetration  insead  of  one  of  65,  as  had  been  previously  the 
case.  The  surface  marked  up  under  traffic  excessively,  however, 
during  the  first  summer  and  aroused  much  comment.  Com- 
munities soon  become  accustomed  to  this  and  the  marking  in 
new  surfaces  is  objected  to  no  longer,  as  it  is  understood  that  the 
pavement  will  eventually  be  a  superior  one.  In  consequence, 
much  of  the  cracking  of  asphalt  surfaces  can  now  be  avoided 
if  they  are  originally  laid  with  sufficiently  soft  bitumen,  and  the 
reason  for  the  ensuing  marking  is  properly  explained  to  the  public. 

Disintegration. — Disintegration  of  the  surface  in  various  parts 
with  the  formation  of  depressions  or  holes  extending  to  the  base 
is  the  commonest  defect  in  asphalt  surfaces.  Many  defects  of 
this  kind  are  attributable  to  faults  of  construction,  but  they  may 
also  be  due  to  unfavorable  environment  with  the  best  of  surface 
mixtures.  Altogether  they  may  be  summed  up  as: 

Deteriorations  or  defects  due  to: 

Weak  foundation — an  extremely  common  cause. 

Inferior  mixture. 


DEFECTS    AND    DETERIORATION.  491 

Action  of  illuminating-gas. 

Action  of  water. 

Uneven  thickness  of  surface  and  constant  pounding  on  depres- 
sions in  an  unbalanced  mixture. 

Weak  Foundation. — An  asphalt  surface  cannot  resist  the  impact  of 
traffic  if  the  foundation  does  not  furnish  adequate  support.  This,  as 
has  been  reiterated  many  times  in  these  pages,  is  one  of  the  most  seri- 
ous causes  of  the  deterioration  of  asphalt  pavements  in  large  cities 
and  where  they  are  subject  to  heavy  traffic  and  moisture.  Any 
vibration  in  the  surface,  especially  under  unfavorable  surface  con- 
ditions such  as  dirt  and  continued  moisture,  is  extremely  liable  to 
result  in  deterioration  of  a  poor  mixture  and  will  aid  in  destroying 
the  best  surface.  A  defect  due  to  weak  foundation  may  be  manifest  in 
many  ways.  The  surface  may  merely  break  up  and  go  to  pieces, 
or  it  may  at  first  merely  separate  into  small  individual  masses 
which  become  rounded  at  their  edges  and  form  a  collective  group 
of  almond-shaped  patches,  which  eventually  go  to  pieces  with  a 
resulting  hole. 

Inferior  Mixture. — Disintegration  due  to  inferior  mixture  has 
been  too  thoroughly  discussed  in  previous  pages  to  necessitate 
a  recurrence  to  the  reasons  therefor.  It  is,  of  course,  in  careless 
work  the  chief  cause  of  defects  in  asphalt  surfaces,  but  too  often 
disintegration  is  attributed  to  a  poor  mixture  which  is  due  entirely 
to  other  causes. 

Action  of  Illuminating-gas. — The  disintegrating  effect  of  the 
action  of  illuminating-gas  is  a  subject  which  has  not  been  consid- 
ered hitherto  in  these  pages.  The  writer  cannot  do  better  than 
by  allowing  Mr.  A.  W.  Dow,  his  successor  in  the  Office  of  Inspector 
of  Asphalt  and  Cements,  in  the  District  of  Columbia,  to  speak  of 
his  experiences  in  Washington  with  this  cause  of  deterioration  of 
asphalt  surfaces,  as  all  that  he  says  applies  as  well  to  other  cities. 
He  writes  as  follows  in  his  report  to  the  Engineer  Commissioner 
of  the  District  of  Columbia,  for  the  fiscal  year  ending  June  30, 
1899: 

"Disintegration  of  pavements  from  the  absorption  of  illuminat- 
ing-gas, escaping  from  leaky  gas-pipes  or  mains  under  the  pave- 
ment: There  are  several  streets  in  the  city  being  ruined  by  this 


492  THE   MODERN    ASPHALT    PAVEMENT. 

means,  and  it  appears  to  be  a  common  thing  in  all  cities  having 
gas.  The  pavements  are  affected  in  very  much  the  same  way  as 
when  disintegrated  by  coal-tar  binder,  except  the  fine  cracks, 
running  parallel  with  the  street,  make  their  appearance  sometime 
before  the  pavement  begins  to  crowd.  Pieces  of  the  surface 
mixture  taken  up  smell  very  strongly  of  illuminating-gas,  and  in 
some  cases  the  gas  can  be  ignited  by  applying  a  match  to  the  under 
surface  when  it  has  just  been  taken  up.  In  nearly  every  case 
enough  gas  will  be  given  off  by  heating  a  small  piece  of  the  affected 
pavement  in  a  tube  to  have  it  flash  by  igniting. 

"  As  it  has  been  doubted  by  some  that  this  disintegration  is 
really  due  to  illuminating-gas,  I  have  made  a  most  thorough  investi- 
gation of  the  subject  and  believe  have  positively  proven  that 
gas  is  the  cause.  Samples  of  pavements  were  obtained  from 
several  affected  spots,  and  in  all  cases  I  have  been  able  to  obtain 
from  them  a  gas  that  exploded  by  passing  an  electric  spark  after 
mixing  with  ah*.  The  method  employed  to  obtain  the  gas  from 
samples  of  the  surface  mixture  was  by  heating  them  under  boiling 
water  and  collecting  the  gas  given  off  in  an  inverted  funnel.  Those 
not  acquainted  with  the  properties  of  asphalts  might  suggest  that 
heating  any  asphalt  to  this  temperature  might  make  it  give  off  a 
gas.  This  is  impossible,  as  an  asphalt  cement  such  as  is  used  in 
paving  will  lose  only  3  or  4  per  cent  at  the  most  on  being  kept  at 
a  temperature  of  400°  F.  for  30  hours,  and  only  an  infinitesimal 
part  of  this  loss  is  a  gas  at  ordinary  temperatures.  To  make  a 
more  practical  demonstration  of  this,  two  samples  of  a  pavement 
were  taken,  one  from  an  affected  spot  and  the  other  from  a  good 
portion  of  the  pavement  about  10  feet  away.  These  samples 
were  treated  under  boiling  water  until  they  ceased  to  evolve  gas. 
The  affected  sample  gave  several  times  more  gas  than  did  the  other. 
On  testing,  the  gas  from  the  good  sample  was  found  to  consist  of 
oxygen  and  nitrogen,  which  was  evidently  just  the  air  from  the 
voids  of  the  pavement.  The  gas  from  the  affected  piece  gave  on 
analysis: 


DEFECTS    AND    DETERIORATION.  493 

Carbon  dioxide 8.4% 

Oxygen 10.8 

Heavy  hydrocarbons 13 . 4 

Carbon  monoxide 0.7 

Hydrogen 6.6 

Methane .2.0 

Nitrogen 58 . 1 

"  Having  now  found  that  a  gas  is  present  in  the  pavement  so 
affected,  let  us  proceed  to  examine  as  to  its  source.  It  cannot  be 
a  natural  gas  or  marsh-gas,  for  there  is  no  analysis  of  such  gases 
on  record  that  contains  appreciable  amounts  of  heavy  hydrocar- 
bons, while  the  gas  from  the  pavement  is  rich  in  these  compounds. 
The  same  would  also  apply  to  sewer  air  or  gas.  The  only 
remaining  source  is  illuminating-gas,  the  analysis  of  which  is 
here  given: 

Carbon  dioxide 0.2% 

Oxygen 0.0 

Heavy  hydrocarbons 12.1 

Carbon  monoxide 25 . 5 

Hydrogen !  39.2 

Methane 23 .0 

Nitrogen 0.0 

"  On  comparing  the  composition  of  the  gas  given  off  from  the 
disintegrating  pavement  with  the  illuminating-gas  it  is  seen  that 
they  are  not  at  all  similar  in  composition.  At  first  glance  it  would 
not  seem  possible  that  the  former  gas  could  originate  from  the 
latter,  but  when  the  properties  of  asphalt  are  considered  it  is  easily- 
explained. 

"  Heavy  hydrocarbons,  to  which  class  asphalts  belong,  are 
known  to  absorb  other  gaseous  hydrocarbons;  the  heavier  the  gas 
the  more  affinity  between  it  and  the  heavy  hydrocarbons.  Know- 
ing this,  the  ingredients  of  the  illuminating-gas  that  asphalt  would 
have  the  greatest  affinity  for  would  be  the  heavy  hydrocarbon 
gases,  a  slight  affinity  for  the  marsh-gas  or  methane,  and  no  affinity 
for  any  of  the  other  ingredients.  If  we  examine  the  ingredients 
of  the  gas  from  the  affected  pavement,  it  will  be  found  to  consist 
of  some  carbon  dioxide,  ah-  that  was  in  the  voids  and  cracks  of  the 
pavement,  and  the  constituents  of  illuminating-gas  with  the  heavy 


494 


THE    MODERN    ASPHALT    PAVEMENT. 


hydrocarbon  gases  very  much  in  excess,  which  is  what  we  would 
expect.  To  practically  demonstrate  that  the  above  takes  place 
when  asphalt  is  in  contact  with  illuminating-gas,  I  took  two  samples 
of  gas  from  a  tap  in  the  laboratory.  One  was  analyzed,  while  the 
other  was  kept  for  several  weeks  in  a  tube  the  interior  of  which 
was  coated  with  asphalt  cement  such  as  is  used  in  pavements, 
after  which  it  was  analyzed.  The  results  of  the  two  analyses  are 
here  given : 


Original 
Gas. 

Gas  after 
Asphalt 
Absorption. 

Carbon,  dioxide  ... 

0  2% 

0  1% 

Oxvsren   . 

0  0 

0  0 

12.1 

7.2 

25.5 

27.3 

39.2 

42.2 

Methane 

23  0 

23  2 

Nitrogen     •                        .  . 

0  0 

0  0 

"  It  is  evident  from  this  that  the  asphalt  cement  has  absorbed 
over  5  per  cent  of  the  heavy  hydrocarbon  gases,  a  little  methane, 
and  practically  nothing  else. 

"  I  have  ascertained  by  experiment  that  one  part  by  volume 
of  asphalt  cement  will  absorb  forty-two  parts  of  illuminating- 
gas  in  somewhat  over  a  month.  I  have  also  practically  shown 
that  asphalt  is  much  softened  by  asborbing  gas,  the  ordinary 
asphalt  cement  becoming  as  soft  as  a  thick  maltha  after  being  in 
an  atmosphere  of  illuminating-gas  for  several  months.  As  to  the 
quantity  of  gas  contained  in  the  affected  pavements  this  of  course 
varies,  but  in  one  instance  1000  c.c.  of  pavement  gave  off  500  c.c. 
of  gas. 

"  There  is  but  one  way  to  stop  the  disintegration  of  a  pave- 
ment from  this  cause,  and  that  is  to  stop  the  leak  of  gas;  for  it 
is  useless  to  patch  the  pavement,  as  it  will  not  be  long  before 
the  patch  disintegrates.  I  have  known  of  cases  where  a  pave- 
ment so  affected  was  repaired  and  in  fourteen  months  the  patches 
were  showing  signs  of  disintegration." 

The  writer's  investigations  have  in  every  respect  confirmed  the 
conclusions  of  Mr.  Dow. 


DEFECTS    AND    DETERIORATION.  495 

Water  Action. — The  action  of  water  on  poor  and  unsatisfactory 
asphalt  surfaces  has  also  been  considered  at  length.  Continued 
standing  or  running  water  will  destroy  the  best  asphalt  surface,  but 
such  a  defect  is  one  which  can  be  avoided  by  proper  provision  for 
the  prevention  of  such  conditions.  The  best  surfaces  will  resist  for 
years  any  reasonable  water  action.  Unfortunately  provisions  for 
preventing  such  action  are  not  always  adequate  either  from  the 
presence  of  a  porous  base,  seepage  from  soil  in  terraces  above  the 
level  of  the  base,  or  poorly  arranged  grades  to  the  actual  surface 
of  the  pavement,  which  permit  water  to  stand  in  the  gutters.  These 
defects,  not  inherent  in  the  pavement  but  merely  in  the  mode  of 
construction,  can  be  readily  provided  against. 

Of  the  results  of  the  action  of  water  reaching  the  asphalt  through 
a  porous  base,  Mr.  A.  W.  Dow  writes  as  follows: 

"  Disintegration  by  Water  Entering  a  Pavement  by  Oozing  up 
Through  the  Base. — I  believe  if  more  thorough  investigation  were 
made  into  the  cause  for  the  disintegrating  of  pavement,  this  would 
be  found  to  be  one  of  the  most  common,  especially  in  small  towns 
and  cities  where  there  are  terraces  or  considerable  lawns  in  front 
of  houses.  There  have  been  a  number  of  cases  in  this  city  where 
the  water  has  entered  a  terrace  or  parking  where  they  were  above 
the  grade  of  the  street  and  worked  its  way  up  through  the  con- 
crete base  to  the  asphalt  surface. 

"  This  disintegration  manifests  itself  differently,  depending 
on  the  character  of  the  pavement.  If  the  asphalt  surface  is  soft 
or  the  concrete  smooth,  the  first  defect  noticed  will  be  the  ten- 
dency of  the  pavement  to  crowd  in  warm  weather.  This  is  due 
to  the  under  portion  of  the  surface  mixture  rotting,  so  to  speak, 
thus  destroying  the  cementing  properties  of  the  asphalt.  The 
upper  portion,  although  good,  being  deprived  of  the  support  of 
the  affected  mixture  under  it,  will  be  crowded  out  by  traffic.  This 
crowding  is  assisted  by  the  concrete  base  being  smooth,  and  also 
the  bond  between  the  base  and  binder  are  destroyed  by  the  moisture. 

"  In  cases  where  the  concrete  base  is  rough  and  the  surface 
mixture  hard,  the  principal  disintegration  will  take  place  in  cold 
weather,  nothing  abnormal  being  noticed  until  the  pavement 
begins  a  rapid  crumbling  away  in  the  affected  spots  under  traffic. 


496  THE    MODERN    ASPHALT    PAVEMENT. 

"  On  examining  a  section  of  asphalt  surface  disintegrating 
from  this  cause,  especially  where  it  has  not  been  going  on  for 
too  long  a  time,  there  will  be  found  a  layer  of  perfectly  sound 
and  good  material  at  the  surface  of  the  pavement,  while  under- 
neath the  mixture  will  show  evidence  of  being  disintegrated  by 
water — that  is,  the  sand  will  appear  clean  and  white  in  spots,  as 
though  there  had  been  an  insufficiency  of  asphalt  cement  to  cover  it. 
The  concrete  base  under  the  affected  pavement  will  generally 
be  found  damp  or  even  wet.  We  have  prevented  the  destruction 
of  several  pavements  from  this  cause  by  the  use  of  blind  drains 
put  in  under  the  gutter  next  to  the  lawn  or  terrace,  and  even 
run  herringbone  under  the  pavement. 

"  This  last  cause  for  disintegration  would,  of  course,  not  occur 
in  a  pavement  constructed  with  an  asphalt  that  was  unacted 
on  by  water,  but  water  soaking  up  through  a  concrete  base  might 
injure  any  pavement  by  freezing. 

"  It  is  always  advisable  where  a  pavement  shows  signs  of  dis- 
integrating to  examine  into  the  cause  in  a  most  careful  manner 
and  not  pass  snap  judgment.  It  seems  only  too  easy  for  the 
majority  of  people,  whether  experienced  or  not,  to  place  the  blame 
for  the  failure  of  a  pavement  on  the  manufacturers.  I  have  heard 
men  with  considerable  experience,  commenting  on  a  bad  place 
in  a  pavement  that  they  had  not  carefully  examined,  remark, 
'  They  used  bad  oil  or  asphalt  in  that  piece  of  work.'  They  have 
not  taken  into  consideration  that  all  but  possibly  a  square  yard 
of  the  pavement  is  in  good  condition  and  that  it  would  be  no 
economy  to  a  contractor  to  use  bad  material  in  one  small  place 
of  the  pavement.  A  careful  examination  into  the  disintegrating 
of  a  pavement  may,  in  many  cases,  show  a  cause  that  is  entirely 
foreign  to  the  composition  of  the  materials  and  a  cause  that  could 
be  easily  remedied  with  a  little  common  sense." 

The  conclusions  of  Mr.  Dow  in  regard  to  such  causes  of  dis- 
integration are  most  reasonable. 

Poor  Workmanship. — The  raking  of  the  hot  asphalt  mixture 
to  an  uneven  thickness  before  compression,  resulting  in  the  forma- 
tion of  depressions  in  the  surface  under  the  final  compression 
obtained  from  traffic  results  in  disintegration  of  the  less  satisfactory 


DEFECTS    AND    DETERIORATION.  497 

mixtures  owing  to  the  constant  impact  of  the  wheels  of  vehicles 
suddenly  dropping  into  such  depressions.  This  is  a  fault  often  due 
to  carelessness  in  construction  and  is  not  a  common  one. 

Scaling  of  Asphalt  Surfaces. — Scaling  of  asphalt  surfaces  has 
been  in  individual  cases  a  serious  cause  of  the  deterioration.  It  is 
something  which  happens  only  in  moist  climates,  particularly  in 
those  near  the  seacoast,  or  where  fogs  are  prevalent,  and  where  it 
is  the  custom  to  water  streets  continually  without  the  removal  of 
the  accumulated  dirt.  It  is  particularly  frequent  with  coarse 
mixtures,  and  hi  order  to  avoid  it  the  grading  of  the  sand,  the 
character  of  the  filler,  the  character  of  the  asphalt  and  flux  in  use, 
their  proper  combination,  together  with  the  support  of  the  resulting 
surface  on  a  base  free  from  vibration,  must  receive  the  most  care- 
ful attention. 

That  the  problem  can  be  successfully  met  has  been  proved  by 
the  fact  that  pavements  which  have  not  suffered  from  scaling 
have  been  laid  on  Broadway  and  Fifth  Avenue  in  New  York,  and 
in  the  foggy  and  damp  climates  of  London,  Glasgow,  and  Paris, 
in  the  first  of  which  cities  the  successful  application  of  the  modern 
asphalt  surface  mixture  was  worked  out  in  1896  after  two  failures, 
to  be  equally  successfully  followed  by  similar  results  later  in  Glas- 
gow and  Paris. 

Scaling  is  characterized  by  the  separation  under  traffic,  when 
the  streets  are  wet  and  the  ah*  so  humid  as  to  prevent  their  drying, 
of  a  thin  film  of  the  asphalt  mixture  from  the  surface  of  the  pave- 
ment. No  satisfactory  explanation  of  this  phenomena  has  been 
advanced.  We  must  content  ourselves  with  noting  its  occurrence. 

After  drying  out  the  asphalt  surface  resumes  its  normal  appear- 
ance, rolling  out  smoothly  under  traffic,  but  the  thickness  of  the 
pavement  is  decreased.  The  same  thing  will  happen  again  under 
like  conditions  until  a  depression  or  hole  is  worn  and  repairs  are 
necessary. 

Enough  is  known,  as  has  been  said,  to  show  that  the  weaker 
poorly  graded  mixtures  lacking  in  bitumen  and  made  with  unsatis- 
factory asphalt  cement  suffer  most  from  scaling.  It  is  also  much 
more  in  evidence  where  the  base  is  weak.  Mixtures  having  a  filler 
of  Portland  cement  are  the  most  resistant,  and  finally  it  never 


498  THE    MODERN    ASPHALT   PAVEMENT. 

occurs  in  a  pavement  thoroughly  well  constructed,  such  as  that 
on  Fifth  Avenue  in  New  York,  or  those  properly  laid  in  London 
and  Paris;  that  is  to  say,  it  can  be  avoided  entirely  if  the  proper 
precautions  are  used.  The  watering-cart  and  lack  of  cleanliness 
are  great  aids  to  the  production  of  scaling  and,  in  fact,  to  the 
general  diminution  of  the  life  of  an  asphalt  pavement,  but  this  is 
a  condition  the  consideration  of  which  must  properly  be  taken  up 
under  the  head  of  the  effect  of  environment  upon  such  surfaces. 

Displacement  of  Asphalt  Surfaces.  —  The  displacement  of 
asphalt  pavements  under  traffic  resulting  in  a  rolling  or  wavy 
surface  was  a  serious  defect  in  the  early  days  of  the  industry. 
It  was  due  to  the  fact  that  the  asphalt  mixtures  were  unbalanced, 
the  mineral  aggregate  was  not  properly  graded,  and  the  bitumen 
was  present  either  in  too  small  or  too  great  an  amount,  with  the 
result  that  the  surface,  not  having  sufficient  internal  stability, 
moved  upon  the  more  or  less  smooth  hydraulic  base,  to  which  it 
was  not  tied  by  any  intermediate  course,  under  the  pressure  and 
impact  of  traffic.  It  has  even  moved  in  cases  where  such  a  course 
exists  where  the  stability  is  unusually  small.  Defects  of  this 
description,  which  were  at  one  time  common,  have  been  avoided 
not  only  by  the  introduction  of  a  binder  or  paint  course,  but  also, 
in  the  few  surfaces  constructed  in  recent  years  without  such  a 
course,  by  the  greater  stability  of  the  surface  mixture. 

Displacement  of  the  surface  and  formation  of  waves  in  asphalt 
surfaces  do,  however,  occur  occasionally  at  present,  and  this 
has  been  found  to  be  due  to  the  percolation  of  water  through  an 
open  binder  course,  and  its  attacking  the  under  surface  of  the 
wearing  surface  of  the  pavement,  thus  reducing  its  stability  and 
permitting  of  the  movement  of  the  upper  portion  of  the  surface 
upon  the  loosened  lower  part.  This  occurrence  is  particularly 
noticeable  where  a  pavement  of  this  form  of  construction  adjoins 
a  street  railway  track  which  is  not  stable,  vibrating  and  admitting 
water  between  the  rail  and  the  pavement.  Such  occurrences 
bring  out  very  strongly  the  injury  to  all  forms  of  pavement,  of 
?.n  unsatisfactory  track  construction,  and  of  the  difficulty  of 
*naintaining  any  pavement  under  such  conditions. 


DEFECTS    AND    DETERIORATION.  499 

Expansion  of  Cement  in  the  Foundation. — The  surface  of  an 
asphalt  pavement  has  been  at  times  raised  transversely  into  waves 
by  the  expansion  of  the  cement  used  in  the  construction  of  the  base 
with  the  direct  result  of  raising  the  latter  at  points  of  least  resist- 
ance generally  at  joints  between  different  days'  work  and  the 
immediate  elevation  of  the  asphalt  surface  above  these  points. 
This  has  occurred  with  both  natural  and  Portland  cement,  but 
usually  with  magnesian  cements  of  the  former  type.  When  the 
expansion  has  ceased  after  the  lapse  of  several  years,  removal  of 
the  excess  of  base  and  replacement  of  the  surface  at  a  normal 
grade  obviates  any  further  trouble. 

Deterioration  of  Asphalt  Pavements  Due  to  Environment. — 
Deterioration  in  asphalt  surfaces  is  brought  about,  even  in  those 
of  the  best  form  of  construction,  or  to  a  much  greater  degree,  of 
course,  in  those  which  are  poorly  constructed,  by  the  nature  of 
the  environment  to  which  they  are  subjected. 

Difficult  climatic  environment  is  something  that  cannot  be 
escaped  and  must  be  met  as  well  as  possible  by  the  form  of  con- 
struction of  the  pavement  and  by  the  character  of  the  surface 
mixture  with  which  the  pavement  is  constructed.  That  this 
must  be  accommodated  to  the  climatic  conditions  which  it  is 
to  meet  is  apparent  and  is  generally  understood,  at  least  as  far 
as  temperature  in  its  relations  to  latitude  is  concerned  and  with 
reference  to  sudden  falls  in  temperature.  The  unfavorable  envi- 
ronment due  to  prolonged  humidity  is,  however,  the  most  serious 
condition  to  be  met,  especially  where  the  traffic  is  heavy,  the  sur- 
face not  kept  clean,  and  the  air  temperature  for  long  periods  lying 
between  freezing  and  45°  F.  As  examples  of  the  former  con- 
dition might  be  cited  the  climate  of  St.  Paul,  Omaha,  and  New 
Orleans. 

In  the  latter  place  it  is  very  necessary  to  make  the  surface 
with  a  bitumen  sufficiently  hard  in  consistency  not  to  prove  unde- 
sirable in  the  summer  months,  as  the  temperatures  in  winter  are 
not  low  enough  to  produce  cracking.  For  this  purpose  a  cement 
of  50  penetration  on  the  Bowen  machine  is  usually  employed. 
In  St.  Paul,  on  the  other  hand,  where  the  winter  temperatures 
are  very  low  a  penetration  of  90  is  used.  A  cement  of  this  degree 


500  THE    MODERN    ASPHALT    PAVEMENT. 

of  softness  will  naturally  result  in  a  pavement  which  marks  up 
to  a  notable  extent  in  the  summer  when  first  laid,  but  this  dis- 
agreeable feature  disappears  after  the  second  winter,  and  such  a 
surface  does  not  crack  as  would  those  laid  with  a  harder  cement. 

A  still  more  difficult  climatic  feature  to  meet  is  that  of  sudden 
drops  in  temperature,  often  as  much  as  50°  in  a  few  hours,  which 
are  met  with  in  cities  like  Omaha.  The  immediate  contraction 
caused  by  such  a  drop  is  so  great  as  to  overcome  the  elasticity 
or  ductility  of  the  bitumen,  and  cracking  can  only  be  prevented 
by  using  in  the  mixture  as  it  is  originally  laid  a  very  soft  asphalt 
cement.  An  example  of  such  a  surface,  that  laid  on  Thirty-ninth 
Street  in  Omaha,  Neb.,  will  serve.  It  was  so  soft  when  it  was 
completed  and  marked  so  freely  that  it  was  not  at  once  accepted 
by  the  city.  To-day  it  is  the  only  pavement  of  its  age  in  that 
city  which  has  not  cracked  and  now  does  not  mark  exceptionally 
under  the  hottest  summer  suns. 

Experience  has  taught  how  these  difficulties  may  be  met  with 
in  the  manner  described,  but  pavements  constructed  by  an  inex- 
perienced contractor,  with  an  unbalanced  mineral  aggregate  which 
will  not  permit  the  use  of  cement  of  sufficiently  soft  consistency, 
will  inevitably  show  cracks  in  a  colder  climate  in  the  course  of 
two  or  three  years. 

A  still  more  serious  climatic  condition  to  contend  with  is  that 
met  with  in  climates  where  there  is  excessive  humidity  in  the  winter 
months.  Where  such  a  condition  exists  only  the  most  carefully 
prepared  surface  mixture  will  resist  the  combined  action  of  moisture 
and  heavy  traffic.  This  was  well  illustrated  in  the  earlier  attempts 
to  lay  asphalt  pavements  in  London,  Glasgow,  and  on  the  north- 
western Pacific  Coast.  It  is  even  met  with  in  some  of  our  cities 
on  the  Atlantic  Coast  where  asphalt  pavements  are  placed  on 
very  heavy-traffic  streets.  Much  of  the  earlier  scaling  in  New 
York  City  was  due  to  humidity  combined  with  temperatures 
between  45°  and  the  freezing-point.  Below  a  freezing  tempera- 
ture scaling  and  disintegration  due  to  this  cause  does  not  take 
place. 

The  deterioration  of  an  asphalt  pavement  caused  by  the  unfavor- 
able environment  produced  by  the  leakage  of  coal-gas  from  gas- 


DEFECTS   AND    DETERIORATION.  501 

mains  is  an  important  one  and  has  already  been  discussed  under 
the  heading  "  Disintegration." 

Attention  has  already  been  called  to  the  fact  that  asphaltic 
paving  mixtures  will  not  withstand  the  constant  action  of  ground 
or  running  water,  and  where  they  are  subjected  to  such  an  environ- 
ment they  will  inevitably  deteriorate  more  rapidly  than  is  necessary. 
The  remedy  for  defects  due  to  the  constant  action  of  water  is 
the  removal  of  the  cause  by  the  introduction  of  proper  provisions 
for  drainage. 

Asphalt  pavements  also  suffer  in  one  or  two  of  our  cities  from 
flushing  with  water  under  a  very  considerable  head  with  a  hose 
and  nozzle.  No  surface  of  any  description  can  be  expected  to 
withstand  such  hydraulic  mining.  If  it  is  carried  on  the  city 
must  expect  to  have  the  cost  of  maintenance  of  its  asphalt  streets 
much  increased  at  the  end  of  the  guarantee  period,  and  this  will 
be  the  greater  the  more  inferior  the  asphalt  surface  mixture  is 
in  the  beginning. 

A  still  greater  cause  of  deterioration  of  asphalt  pavements 
is  found  in  the  lack  of  cleanliness  and  general  neglect.  If  the 
pavements  are  not  carefully  cleaned  and  filth  is  allowed  to  lie 
upon  the  surface  for  a  great  length  of  time,  becoming  mud  as 
soon  as  they  are  sprinkled  or  rained  upon,  the  deterioration  is 
very  rapid  and  even  worse  than  when  they  are  subjected  to  the 
action  of  clean  water.  Permitting  mud  and  slime  to  remain  upou 
an  asphalt  surface  displays  great  ignorance,  upon  the  part  of  pub- 
lic officials  of  the  nature  and  behavior  of  asphalt  pavements  and 
should  never  be  allowed  to  take  place.  For  the  same  reason 
asphalt  pavements  should  never  be  sprinkled  if  possible/  The 
dirt  should  be  removed  and  the  situation  not  temporized  with  it 
by  converting  it  into  a  slimy  mud.  This  is  doubly  the  case  since 
such  a  slimy  coating  results  in  making  the  pavement  extremely 
slippery,  a  feature  not  inherent  in  the  asphalt  surface  itself,  but 
attributable  only  to  the  film  of  mud. 

Finally,  asphalt  surfaces  in  cities  like  New  York,  suffer  enor- 
mously from  the  constant  disturbance  to  which  they  are  subjected 


502  THE    MODERN   ASPHALT    PAVEMENT. 

by  being  taken  up  in  connection  with  underground  work.  Though 
an  asphalt  pavement  can  be  repaired  more  readily  than  any  other, 
its  constant  removal  and  renewal  cannot  but  injure  it,  as  the 
foundation  in  such  cases  is  never  as  rigid  as  the  original.  It  can 
be  asserted  without  doubt  that  not  only  asphalt  pavements,  but 
all  others  in  a  large  city,  can  never  be  kept  in  a  state  of  perfect 
maintenance  until  pipe  galleries  are  provided  under  the  streets 
which  shall  do  away  with  the  constant  opening  of  the  surface. 
In  some  of  the  streets  of  New  York,  from  one-third  to  more  than 
the  entire  area  of  the  street  has  been  often  renewed  in  the  course 
of  the  guarantee  period  for  this  reason. 

Deterioration  Due  to  Natural  Wear  and  Neglect  of  Mainte- 
nance.— An  asphalt  surface  is  naturally  more  or  less  deteriorated 
by  usage,  like  all  materials  of  construction,  and  the  amount  which 
it  suffers  in  this  respect  depends  entirely  upon  the  character  of 
the  original  workmanship  and  the  traffic  and  other  conditions  to 
which  it  is  to  be  exposed.  Some  asphalt  pavements  under 
light  traffic,  such  as  that  opposite  the  Arlington  Hotel  in 
the  city  of  Washington,  have  given  good  service  for  30  years 
and  may  be  expected  to  last  much  longer.  On  the  heaviest 
traffic  streets  constructed  with  the  greatest  skill  some  minor 
repairs  may  be  expected  at  the  end  of  from  3  to  5  years,  depend- 
ing upon  the  rigidity  of  the  base  which  supports  the  surface 
and  upon  the  manner  in  which  these  repairs  are  made,  the 
extent  of  its  deterioration  will  largely  depend.  The  question  of 
maintenance  will  be  discussed  in  the  following  chapter. 

SUMMARY. 

To  the  general  reader  the  preceding  chapter  will  probably  be 
one  of  the  most  interesting  and  instructive  in  the  book,  and  it  should 
be  read  in  detail,  as  it  explains  the  reasons  for  defects  in  and  the 
causes  of  the  deterioration  in  asphalt  surfaces.  The  chapter  may  be 
summarized  briefly  as  follows : 

Defects  in  asphalt  pavements  are,  to  the  greatest  extent,  to  be 
attributed  to  faults  of  construction. 


DEFECTS   AND    DETERIORATION.  503 

1.  Due  to  improper  specifications  for  the  form  of  construction, 
the  fault  of  the  city  officials. 

2.  Due  to  careless  construction  on  the  part  of  the  contractor, 
and  also 

3.  To  improper  maintenance  when  the  age  of  the  pavement  is 
such  that  it  should  be  given  careful  attention,  as   unfortunately 
the  American  public  and  many  city  officials  seem  to  believe  that 
when  a  street  is  once  paved  it  should  be  expected  to  last  forever 
without  maintenance. 

4.  The  action  of  illuminating-gas  escaping  from  the  mains. 

5.  Constant  opening  for  underground  work. 


CHAPTER  XXVI 
MAINTENANCE  OF  ASPHALT  PAVEMENTS. 

THE  question  of  the  proper  maintenance  of  asphalt  pavements 
demands,  but  has  not  received,  very  careful  consideration  on 
the  part  of  most  of  our  municipalities  and  municipal  officials, 
but  it  fortunately  is  receiving  more  to-day  than  in  the  past.  Owing 
to  the  fact  that  asphalt  pavements  have  generally  been  laid  under 
guarantees  by  the  contractor  for  their  maintenance  for  a  con- 
siderable period,  a  custom  which,  as  has  been  said,1  is  rapidly 
disappearing,  too  little  consideration  has  'been  given  to  their 
maintenance  after  its  expiration.  As  a  result  of  this,  they  have 
deteriorated  very  rapidly  when  thrown  upon  the  hands  of  the 
municipality,  and  their  condition  has  become  such  as  to  cause 
very  unfavorable  comment  and  great  dissatisfaction.  In  a  few 
cities,  such  as  Washington,  D.  C.,  it  has  been  demonstrated  that 
there  is  no  difficulty  in  maintaining  an  ordinary  asphalt  street 
in  good  condition  for  from  15  to  20  years,  at  a  moderate  cost, 
as  has  been  shown  by  Capt.  H.  C.  Newcomer  in  a  report  published 
in  the  Engineering  News  for  February  18,  1904,  where  he  shows 
that  of  the  2,425,732  square  yards  of  bituminous  pavements 
maintained  by  that  city,  of  which  not  less  than  2,161,181  square 
yards  are  laid  with  Trinidad  Lake  asphalt,  the  cost  of  main- 
tenance was  as  follows,  the  average  age  of  the  surfaces  being 
about  14.8  years,  while  there  are  over  700,000  square  yards  that 
are  over  18  years  of  age.  He  also  shows  that  the  average  age 

1  See  page  445. 

504 


MAINTENANCE   OF   ASPHALT   PAVEMENTS. 


505 


of  the  areas  resurfaced  during  the  fiscal  year  ending  July  1,  1903, 
was  21  years,  and  this  may  be  regarded  as  well  within  the  limits 
of  the  duration  of  a  standard  asphalt  pavement,  if  it  is  properly 
maintained  during  the  period,  especially  as  the  older  mixtures 
laid  in  Washington  were  by  no  means  up  to  the  standard  of  ex- 
cellence of  those  which  are  now  being  put  down. 

tlOST  OF  MAINTAINING  ASPHALT  PAVEMENTS  OF  VARIOUS 
AGES  AT  WASHINGTON,  D.  C. 


Age  in  Years. 

Area, 
Square  Yards. 

Cost  of  Repairs 
for  the  Year. 

Average  Cost  per 
Square  Yard 
per  Year. 

5       

1,841,435 

$11,897 

$0  0065 

6  

1,809,869 

13,965 

0077 

7  

1,747,461 

31,385 

0180 

8  

1,653,811 

38,531 

0233 

9  

1,597,313 

42,871 

.0269 

10     

1,476,575 

38500 

0260 

11  

1,1|2,200 

43,003 

0333 

12  

1,068,848 

42,270 

.0396 

13  

913,795 

31,546 

.0345 

14  

804,420 

28,435 

.0354 

15          

698,826 

21  576 

0309 

16  

608,117 

23,479 

0386 

17  

560,823 

18,913 

0338 

18  

504,995 

23,012 

0456 

19     

374,800 

11  951 

0319 

20  

272,040 

7,182 

0264 

21  

192,643 

3,879 

0201 

22  

104,001 

2,887 

0280 

23  

36,332 

678 

0187 

24     

35,647 

1,268 

0356 

Neglect  of  maintenance,  however,  has  resulted  in  quite  a 
different  condition  in  many  other  cities.  There  are  one  or  two 
cities  in  the  United  States  where,  at  the  expiration  of  the  guarantee 
period,  no  attempt  is  made  at  further  maintenance,  and,  as  a 
result,  the  asphalt  pavements  in  these  cities  in  a  few  years  are 
in  a  wretched  condition,  arousing  comment  and  adverse  criticism 
of  this  form  of  pavement  on  the  part  of  all  the  citizens.  This 
can  in  nowise  be  attributed  to  the  character  of  the  pavement 
itself,  but  to  the  narrow  policy  pursued  by  the  public  officials  in 
charge  of  the  streets.  Nothing  can  be  so  far  from  economical 


506  THE    MODERN   ASPHALT    PAVEMENT. 

as  to  allow  an  asphalt  pavement  to  go  without  repairs  when  they 
are  needed,  as,  in  this  case  as  in  all  others,  a  '  'stitch  in  time  saves 
nine." 

On  the  other  hand,  there  are  numerous  cities,  such  as  Phila- 
delphia and  Washington,  which  have  met  with  no  difficulty 
whatever  in  maintaining  their  asphalt  pavements  in  good  condition 
under  the  contract  system,  a  proper  amount  of  funds  being  made 
available  in  the  spring  of  the  year.  In  at  least  one  other  city 
where  the  money  is  not  available  until  mid-summer,  July  1st, 
the  contract  system  has  not  proved  as  desirable.  In  several  cities, 
the  failure  of  the  contract  system  has  been  due  more  to  the  pro- 
miscuous way  in  which  cutting  up  of  the  pavement  is  permitted 
by  the  city  authorities,  than  to  the  manner  in  which  repairs  are 
made. 

This  situation  has  been  discussed,  as  far  as  maintenance  is 
concerned,  in  an  article  by  Mr.  S.  Whinery,  in  Engineering  News 
for  May  9,  1907.  He  says  in  psfk: 

"  It  cannot  be  denied  that  the  condition  of  asphalt  pavements 
in  most  cities  is  unsatisfactory,  while  in  many  it  is  deplorable  and 
is  rapidly  becoming  intolerable.  To  attribute  this  condition  to 
inherent  inferiority  of  this  kind  of  pavement,  as  many  people  do, 
is  wholly  unwarranted.  Everything  considered,  a  well  constructed 
and  properly  maintained  asphalt  pavement  is  not  inferior  to  any 
other  kind  of  pavement  now  in  use.  At  the  same  time  it  must  be 
conceded  that  an  asphalt  pavement  usually  requires  attention  and 
repairs  at  an  earlier  period  in  its  life  than  most  of  the  other  pave- 
ments in  common  use,  and  it  is  probable,  though  not  yet  certain, 
that  the  total  cost  of  maintenance  during  its  useful  life  is  also 
somewhat  greater.  It  is  certain  that  it  requires  more  frequent 
and  careful  attention  during  its  life  to  keep  it  in  a  proper  state  of 
repair  than  do  stone  or  brick  pavements.  It  is  often  the  case 
that  high  grade  articles  or  structures  require  more  careful  and 
skillful  attention  than  the  cruder  varieties  of  the  same  class. 
It  will  certainly  not  be  claimed  that  the  value  of  a  pavement 
may  be  measured  by  the  amount  of  neglect  and  abuse  it  will 
endure." 

"As  the  first  important  step  in  this  direction  the  city  must 


MAINTENANCE    OF    ASPHALT  PAVEMEN*S.  507 

avoid,  in  the  contract  and  specifications,  requirements  that  are 
indefinite  and  ambiguous,  and  under  which  the  contractor's 
duties  cannot  be  clearly  determined  and  enforced.  We  have 
seen  that  the  long  guaranty  involves  inherent  conditions  which, 
under  the  above  stipulation,  it  is  necessary  to  avoid.  It  should 
therefore  be  omitted  from  all  future  contracts.  The  art  of  con- 
structing asphalt  pavements  is  now  so  well  understood  that  it 
is  entirely  possible  to  frame  and  administer  specifications  that 
will  insure  the  production  of  a  first  class  pavement,  and  the  con- 
ditions that  originally  dictated  these  guarantees  therefore  no 
longer  exist.  The  attempt  thus  to  make  the  contractor  responsible 
for  the  character  of  the  work  he  does  has  not,  in  practice,  been 
found  effectual;  moreover,  our  present  knowledge  of  how  the 
work  should  be  done  and  the  practicability  of  thorough  inspection 
and  supervision,  renders  the  resort  to  such  an  expedient  largely 
unnecessary.  But  if  a  time  guaranty  is  still  thought  advisable, 
the  period  may  be  made  so  comparatively  short  that  questions  of 
faulty  construction  shall  not  be  confused  with  those  of  mainte- 
nance. Barring  accidental  and  unusual  injuries,  maintenance 
questions  ought  not  to  arise  within  a  period  of  two  years  after  the 
completion  of  the  construction  work,  while  palpable  construction 
faults  should  be  revealed  within  that  time.  The  guaranty 
period  should  not  therefore,  exceed  two,  or  at  the  most,  three 
years.  Maintenance  after  that  period  ^should  be  provided  by 
the  city." 

Surface  Heaters. — The  question  of  the  best  way  to  maintain 
an  asphalt  pavement  lies  between  cutting  out  the  entire  surface 
and  binder,  and  ihe  use  of  what  are  known  as  '  'surface  heaters," 
which  consist  of  a  machine  which  directs  a  blast  of  flame  from  a 
series  of  naphtha  burners  upon  the  asphalt  surface  and  softens 
it  so  that  it  can  be  removed  to  such  depth  as  may  be  necessary 
to  reach  undisintegrated  material,  and  then  applying  sufficient 
fresh  material  upon  the  area  thus  laid  bare  to  renew  the  pavement 
to  proper  thickness.  Such  work  has  been  extremely  satisfactory 
in  the  past.  As  an  example,  the  surface  of  Madison  Avenue, 
between  23d  and  26th  Streets,  in  New  York  City,  was  entirely 
replaced  in  this  manner  in  1895,  and  has  remained  in  excellent 


508  THE   MODERN    ASPHALT   PAVEMENT. 

condition  up  to  the  present  time.  Of  course  the  work  cannot 
be  done  in  wet  or  cold  weather.  At  such  periods  the  entire  sur- 
face where  disintegration  occurs  must  be  cut  out  to  the  foundation. 
The  surface  heater  work  is  of  course  much  more  economical. 

Under  any  circumstances,  all  maintenance  and  repair  work 
will  require  the  greatest  skill  in  their  execution,  and  too  much 
care  cannot  be  devoted  to  the  details  of  it. 


PART  IX. 
CONTROL  OF  WORK. 


CHAPTER  XVII. 

INSTRUCTIONS  FOR  COLLECTING  AND  FORWARDING  TO  THE 
LABORATORY  SAMPLES  OF  MATERIALS  IN  USE  IN  CON- 
STRUCTING ASPHALT  PAVEMENTS. 

IN  order  that  a  laboratory  examination,  which  has  already  been 
shown  to  be  necessary,  may  be  satisfactorily  carried  out  the  samples 
which  are  collected  for  this  purpose  should  be  carefully  taken  and 
according  to  some  system. 

The  following  directions  have  been  prepared  by  the  author  for 
the  use  of  superintendents  and  yard  foremen. 

The    materials    for   the    construction    of    asphalt    pavements 
which  require  inspection  in  the  laboratory  may  be  classified  as 
follows: 
IN  USE  IN  FOUNDATION. 

Broken  stone,  gravel,  sand,  hydraulic  cement. 
IN  USE  IN  BINDER. 

Broken  stone,  bituminous  cement. 
IN  USE  IN  SURFACE. 

Stone  for  asphaltic  concrete,  sand,  dust,  or  filler,  refined  asphalt, 
fluxing  agents,  either  eastern  residuum,  California  asphaltic 
oil,  or  other  similar  substances,  and  prepared  from  these 
materials,  asphalt  cement  and  the  surface  mixture  itself. 

509 


510  THE    MODERN    ASPHALT    PAVEMENT. 

These  materials  should  be  of  satisfactory  quality,  and  in  order 
to  determine  this,  samples  should  be  sent  for  examination  and 
report  to  the  New  York  Testing  Laboratory,  Maurer,  N.  J.  Fol- 
lowing are  directions,  which  must  be  closely  observed,  for  collect- 
ing and  forwarding  these  samples  from  every  city  where  contracts 
are  made  and  under  way. 

Samples  and  Specimens. — §  1.  To  begin  with,  it  must  be 
explained  that  there  is  a  decided  difference  between  a  sample 
and  a  specimen  of  any  material.  A  specimen  is  some  of  the  mate- 
rial selected  to  show  its  prominent  characteristics,  either  of  an 
inferior  or  desirable  nature.  A  sample,  if  properly  taken,  represents 
the  average  composition  and  character  of  the  material  it  represents. 

Specimens  are  preferable  to  samples  in  certain  instances  and 
the  reverse.  When  it  is  desired  to  emphasize  the  peculiarities  of 
some  material,  a  specimen  is  needed;  but  when  a  quantitative 
determination  of  its  characteristics  is  to  be  made,  a  sample  is 
necessary. 

This  distinction  must  be  borne  in  mind  in  sending  materials 
to  the  laboratory  for  examination,  and  good  judgment  must  be 
used  in  regard  to  the  most  satisfactory  means  of  arriving  at  the 
desired  end. 

Materials  for  Foundation. — §  2.  No  samples  of  broken  stone, 
sand,  or  cement  need  be  forwarded,  unless  there  is  some  question  as 
to  their  suitability  or  quality,  or  unless  they  fail  to  meet  the  approval 
of  the  local  engineers.  Under  the  latter  circumstance,  two  or 
three  fragments  of  broken  stone,  a  small  sample  box  of  sand,  or 
four  pounds  of  hydraulic  cement  should  be  sent  to  the  laboratory, 
carefully  identified  as  to  the  source  from  which  the  material  comes 
and  as  to  the  parties  furnishing  the  same. 

Materials  for  Binder. — §  3.  No  samples  of  broken  stone  or  gravel 
for  binder  need  be  forwarded  unless  their  quality  be  in  question. 
Samples  of  asphalt  cement  for  binder  should  be  sent  in  the  same 
way  as  those  for  surface  mixture,  if  especially  made  for  binder. 

Materials  for  Surface  Mixture. — §  4.  Sand. — In  the  case  of 
sand  supplies  which  have  not  been  previously  in  use,  and  in  every 
case  at  the  beginning  of  a  new  season's  work,  samples  of  the  one 


SAMPLES  OF  MATERIALS  FOR  THE  LABORATORY.       511 

or  more  sands  the  use  of  which  is  proposed,  or  information  in 
regard  to  the  nature  of  which  is  desired,  should  be  sent  to  the 
laboratory  with  definite  statements  as  to  source,  whether  river, 
lake,  bank,  etc.,  with  the  name  of  the  party  furnishing  it  and  the 
locality  in  which  the  sand  is  found.  These  samples  should  weigh 
from  two  to  three  pounds,  as  much  as  will  fill  a  cigar-box  holding 
fifty  cigars.  The  sample  should  be  moistened  and  tightly  packed 
so  that  the  finer  sand  particles  cannot  sift  out  and  be  lost. 

Samples  of  sand  supplies  which  have  been  approved  need 
not  be  sent  again  during  the  same  season,  unless  the  character 
of  the  deliveries  appears  to  have  changed  decidedly  or  is  sus- 
pected to  have  done  so. 

Samples  of  the  sand  in  use  on  the  platform,  after  it  has  been 
heated  and  screened  should  be  sent  to  the  laboratory  once  a  week, 
when  the  plant  is  running.  The  quantity  contained  in  the  ordinary 
screw-top  tin  sample  box  is  sufficient  in  this  case  unless  other- 
wise directed. 

§  5.  Dust  and  Filler. — The  ground  mineral  matter,  or  dust, 
proposed  for  use  as  a  filler  should  be  sent  in  whenever  a  new 
source  of  supply  is  contemplated,  and  its  use  not  begun  until  its 
quality  has  been  approved. 

From  each  delivery  of  such  material  a  sample  should  be  for- 
warded for  examination. 

The  amount  contained  in  an  ordinary  tin  sample  box  is,  in 
either  case,  sufficient  for  this  purpose. 

§  6.  Refined  Asphalt.  —  Of  refined  Trinidad  or  Bermudez 
asphalt  it  is  unnecessary  to  send  samples  from  the  paving  plants, 
as  this  material  has  usually  been  inspected  at  the  refineries.  If, 
however,  a  shipment  or  any  part  of  it  appears  to  be  of  inferior 
quality  or  dirty,  a  convenient  sized  specimen,  showing  the  defects 
noticed,  should  be  provided  for  examination. 

Asphalt  from  any  other  source  which  may  happen  to  be  in 
use,  either  experimentally  or  otherwise,  should  be  sent  in  for 
examination  in  the  form  of  a  convenient  sized  representative 
specimen. 

§  7.  Fluxing  Agents. — A  sample  of  each  shipment  or  tank 
car  of  residuum,  California  soft  asphalt  or  similar  material  in  use 


512  THE    MODERN    ASPHALT    PAVEMENT. 

for  softening  the  hardei  asphalts  in  making  asphalt  cementr 
should  be  sent  in  a  tin  can  by  express,  not  less  than  a  pint  in 
amount. 

Materials  similar  to  blown  oils  can  be  sent  in  a  box. 

§  8.  Asphalt  Cements.  —  Samples  of  asphalt  cements  from 
every  tank  that  is  put  in  use  should  be  taken  at  that  time  and  for- 
warded to  the  laboratory.  If  the  consistency  of  that  tank  of 
cement  becomes  altered  at  any  time  during  the  day  by  the  addi- 
tion of  oil  or  flux,  a  new  sample  should  be  taken. 

If  the  asphalt  cement  in  any  tank  is  not  exhausted  in  one 
day's  run,  and  is  in  use  again  one  or  more  days  afterwards,  samples 
for  each  of  these  days  should  be  taken  and  sent  to  the  laboratory, 
stating  at  the  same  time  on  a  postal  card,  giving  the  number  of 
the  sample,  the  amount  of  oil  or  flux  that  has  been  added  per  every 
hundred  pounds  of  cement  estimated  to  be  in  the  tank  or  dipping- 
tank  at  the  time  the  oil  was  added.  The  screw-top  tin  sample 
boxes  are  to  be  used  for  this  purpose. 

§  9.  Surface  Mixture. — Samples  of  surface  mixture  should 
be  forwarded  daily.  For  ordinary  work  one  is  sufficient,  but 
where  an  important  piece  of  work,  subject  to  trying  conditions, 
is  completed  in  one  day,  two  or  three  samples,  taken  at  intervals 
while  the  mixture  is  being  sent  out,  should  be  sent,  to  better  illustrate 
the  average  composition  of  the  surface. 

Sampling  Methods  to  be  Employed. — §  10.  Unless  the  sampling 
of  any  material  that  is  to  be  examined  is  carefully  done,  the  sample 
will  not  be  a  representative  one,  and  all  work  done  upon  it  will  be 
wasted.  The  results  will  be  worse  than  useless — that  is  to  say, 
deceiving.  Too  much  emphasis  cannot  be  placed,  therefore,  on 
the  necessity  for  great  care  in  this  direction.  In  addition  to 
what  has  already  been  said  in  regard  to  sending  samples  to  the 
laboratory,  the  following  suggestions  for  taking  them  should  be 
followed  closely. 

§  11.  SAMPLING  SAND: 

1st.  From  Pit  or  Bank. — It  must  be  borne  in  mind  that  in  a 
pit  or  bank  the  sand  lies  in  layers  of  different  grading,  which  can 
almost  never  be  taken  out  separately.  Experience  has  shown 
that  the  best  that  can  be  done  is  to  obtain  a  supply  representing 


SAMPLES  OF  MATERIALS   FOR  THE  LABORATORY.       513 

the  average  composition  of  the  face  of  the  bank.  It  is  useless, 
therefore,  to  send  specimens  of  sand  from  strata  that  cannot  be 
isolated;  or,  if  they  are  sent,  specimens  of  the  other  layers  in  the 
bank  should  accompany  them,  with  a  statement  of  their  relative 
thickness.  A  proper  sample  can  be  obtained  by  cutting  a  groove 
down  the  face  of  the  bank  and  collecting  the  material  in  a  pile 
and  sampling  as  described  below. 

2d.  From  Rivers  or  Lakeshores. — In  case  it  is  desired  to  sample 
sands  from  river  bottoms  or  lakeshores,  it  is  impossible  hi  ordinary 
cases  to  send  in  more  than  what  is  considered  to  be  a  representative 
specimen  of  the  material,  and  final  sampling  must  await  deliveries 
on  scow  or  car. 

3d.  Deliveries  of  Sand  should  be  sampled  as  follows:  Small 
scoopfuls  or  shovelfuls  are  taken  from  different  parts  of  the  pile, 
car,  or  boat  load,  and  at  different  depths,  in  such  number  as  will 
fairly  represent  the  lot,  three  to  six,  from  a  canal-boat  or  barge 
and  at  depths  of  a  foot  or  more,  two  from  a  car,  and  more  or  less 
from  a  pile,  depending  on  its  size.  When  the  sand  is  in  a  pile 
the  coarser  grains  will  have  rolled  to  the  bottom,  so  care  must  be 
exercised  not  to  take  the  sand  from  that  point  or  the  top  alone.  It 
is  also  well  to  dig  some  distance  into  the  heap  for  some  scoop- 
fuls. 

All  the  sand  thus  collected  is  dried,  and,  if  large  in  amount, 
is  made  into  a  heap,  cut  back  and  forth  with  shovels  like  a  batch 
of  concrete  and  quartered,  all  but  one  quarter  being  rejected. 
This  is  continued  until  the  heap  is  reduced  to  such  a  size  that  it 
can  be  passed  through  a  Clarkson  sampler,  found  at  some  of  the 
works,  or  sampled  by  rolling  first  in  one  direction  and  then  at 
right  angles  on  brown  paper  and  halving  the  mass,  this  being  done 
several  times  until  it  is  reduced  to  the  required  size  for  shipping. 

4th.  Sand  from  Platform. — Samples  of  the  hot  screened  sand 
in  use  in  the  mixer  should  be  taken  from  the  spout  of  the  sand- 
bin  while  the  sand  is  running  out  freely  into  the  box  in  the 
process  of  filling  it.  It  should  be  collected  by  running  a  shovel  or 
scoop  back  and  forth  several  times  along  the  edge  of  the  distribu- 
tor and  then  sampling  the  lot  so  gathered,  either  in  a  Clarkson 
sampler  or  by  rolling  on  paper  in  the  usual  way.  , 


514  THE  MODERN  ASPHALT  PAVEMENT. 

Where  there  is  no  sand-bin  a  sample  may  be  taken  from  the 
floor  pile,  as  already  described  from  a  delivery  pile. 

§  12.  For  sampling  material  of  larger  size,  such  as  a  barrel 
of  refined  Trinidad  asphalt,  it  should  be  broken  up  on  a  tarpaulin 
and  reduced  to  a  size  so  fine  that  it  can  be  treated  in  the  same 
way  as  sand.  Usually,  as  has  been  said,  specimens  only  of  rock, 
gravel,  refined  asphalt,  and  such  materials  are  sufficient. 

§  13.  Sampling  Asphalt  Cement. — It  is  difficult  to  always 
obtain  uniform  samples  of  asphalt  cement.  From  the  same 
bucket  samples  have  been  taken  which  varied  as  much  as  six 
points  in  penetration,  owing  to  imperfections  in  the  way  it  was 
dipped,  a  dirty  bucket,  or  lack  of  uniformity  in  the  cement.  Great 
care  should  be  used,  therefore,  to  see  that  none  of  the  conditions 
surrounding  the  dipping  is  abnormal.  The  dipping-bucket  should 
be  immersed  in  the  cement  until  it  is  of  the  same  temperature, 
and  should  then  be  moved  about  rapidly  and  submerged  upside 
down  and  full  of  air  to  the  middle  depth  of  the  still  and  then 
turned  over,  filled,  withdrawn,  and  the  tin  sample  boxes  filled 
where  dust  cannot  reach  them. 

§  14.  Sampling  Surface  Mixture. — A  small  wooden  paddle 
with  a  blade  3  to  4  inches  wide,  5  or  6  inches  long,  and  \  an  inch 
thick,  tapered  to  an  edge  at  one  end  and  with  a  convenient  handle 
at  the  other,  is  used  to  take  as  much  of  the  hot  mixture  from  the 
wagon  as  it  will  hold,  being  careful  to  avoid  any  of  the  last  drop- 
pings from  the  mixer  which  may  not  be  entirely  representative 
of  the  average  mixture.  Samples  of  mixture  should  never  be 
taken  from  the  mixer  itself,  but  only  from  the  wagon  after  mixing 
is  completed. 

In  the  meantime  a  piece  of  brown  manilla  paper  with  a  fairly 
smooth  surface,  10  or  12  inches  wide,  and  torn  off  at  the  same 
length  from  a  roll  of  this  paper,  which  can  be  had  at  any  paper 
warehouse,  is  creased  down  the  middle  and  opened  out  on  some 
very  firm  and  smooth  surface  of  wood,  not  stone  or  metal,  which 
would  conduct  heat  too  rapidly.  The  hot  mixture  is  dropped 
into  the  paper  sideways  from  the  paddle  and  half  of  the  paper 
doubled  over  on  it.  The  mixture  is  then  pressed  down  flat  with 
a  block  of  wood  of  convenient  size  until  the  surface  is  flat.  It 


SAMPLES  OF  MATERIALS  FOR  THE  LABORATORY.       515 

is  then  struck  five  or  six  sharp  blows  with  the  block,  until  the 
pat  is  about  a  £  inch  thick.  The  paper  should  then  be  opened 
and  the  pat  trimmed  with  an  ordinary  table  knife  or  spatula  to  a 
size  of  about  2£  by  4  inches,  and  a  crease  made  along  the  narrower 
edge  at  a  distance  of  J  an  inch  to  facilitate  breaking  off  a  piece 
for  analysis  when  the  pat  is  cold.  Before  the  mixture  is  entirely 
cold  the  proportions  of  sand,  dust,  and  asphalt  cement,  together 
with  the  sample  number,  date,  and  abbreviation  of  the  name 
of  the  city  where  the  sample  is  taken,  is  impressed  upon  it  with 
steel  stamps  in  letters  and  figures  }  of  an  inch  high.  The  paper 
is  also  marked  with  a  rubber  stamp,  identifying  it  with  the  pat. 
Additional  information  as  to  street,  kind  of  dust,  asphalt, 
etc.,  can  also  be  provided  for  in  blank  spaces  opposite  headings 
printed  by  the  rubber  stamp.  Such  a  stamp  may  be  arranged 
as  follows: 


Name  of  city.  .  . , 
Sample  number.  . 
Date  and  hour.  .  . 

Street 

Sand,  coarse 

Sand,  medium.  . . 

Sand,  fine 

Filler,  kind 

A.  C 

Asphalt,  source.  . 

Flux,  kind 

Penetration  A.  C. 
Temperature.  . .  . 


The  pat  papers  should  be  wrapped  about  the  pat  when  cold 
and  both  placed  in  a  heavy  clasp  envelope  for  mailing  at  fourth- 
class  rates. 

The  pat  paper  is  sent  because  the  stain  made  upon  it  by  the 
asphalt  of  the  hot  mixture,  when  considered  in  connection  with 
the  temperature  of  the  mixture  as  it  goes  on  the  street,  is  of  great 
value  in  determining  whether  a  suitable  amount  of  bitumen  is 
present.  Nothing  should  be  written  on  the  pat  paper,  as  this 
renders  the  entire  pat  liable  to  letter  rates  in  mailing,  but  the 
information  required  may  be  sent  by  filling  in  the  blanks  furnished 


516  THE  MODERN  ASPHALT  PAVEMENT. 

by  the  rubber  stamp  on  a  postal  card  and  mailing  this  at  the 
same  time. 

§  15.  Samples  of  Old  Asphalt  Surfaces. — Where  the  determina- 
tion of  the  characteristics  of  an  old  asphalt  surface  is  desired  a 
piece  of  the  surface,  together  with  the  adhering  binder  course, 
if  one  has  been  used,  is  selected  which  will  represent  the  average 
condition  of  the  street.  This  should  weigh  at  least  1  pound,  and 
it  is  generally  desirable  that  two  or  more  samples  from  each  street 
should  be  taken. 

Collecting  Samples.— §  16.  Samples  of  stone,  cement,  sand, 
refined  asphalt,  flux,  etc.,  can  be  taken  by  any  one  about  the 
plant  who  is  competent  to  follow  the  directions  which  have  been 
given  but  samples  of  mixture  and  asphalt  cement  should  be  taken 
by  the  plant  foreman  himself  and  by  no  other  person.  When 
there  is  a  sub-laboratory  at  a  paving  plant  the  chemist  in  charge 
will  have  general  supervision,  and  may,  if  requested  by  the  plant 
foreman,  attend  to  the  collection  of  samples.  The  plant  foreman 
will  be  held  responsible  in  all  cases,  through  the  local  superin- 
tendent, for  the  representative  nature  of  the  samples  or  speci- 
mens which  are  forwarded  to  the  laboratory  and  for  any  deviation 
from  the  preceding  instructions.  It  is  especially  urged  upon  the 
superintendents  that  they  shall  see  that  these  instructions  are 
carried  out,  and  it  is  suggested  that,  to  fully  benefit  by  the  results 
of  the  laboratory  examinations,  samples  should  be  sent  not  only 
of  the  best  but  of  the  poorest  work  at  each  plant,  in  the  latter 
case  calling  attention  to  that  fact  and  giving  the  cause  of  the 
defect. 

It  is  recommended  that  superintendents  require  their  plant 
foremen  to  initial  all  reports  from  the  laboratory  in  order  that  it 
may  appear  that  the  information  given  there  has  been  brought  to 
their  attention. 

Samples  of  asphalt  cement  and  surface  mixture  should  usually 
be  taken  as  soon,  after  starting  up  the  plant,  as  the  work  is  going 
on  regularly.  The  dipping-tank  may  be  sampled  at  once  so  as 
to  be  able  to  mail  it,  as  soon  as  cool,  at  an  early  hour.  Any  change 
in  the  character  of  the  cement  or  addition  to  it  demands  a  new 
sample,  coupled  with  details  of  the  change.  If  a  second  lot  of 


SAMPLES  OF  MATERIALS  FOR  THE  LABORATORY.       517 

cement  goes  into  use  later  in  the  same  day  this  should  also  be 
sampled  immediately  and  sent  to  the  laboratory  as  soon  as  possible. 

A  second  sample  of  mixture  should  be  taken  if  any  decided 
change  in  it  is  made,  such  as  increasing  or  decreasing  the  amount 
of  asphalt  cement,  dust,  or  proportions  of  different  sands. 

The  capacity  of  the  laboratory  for  work  is  large,  and  if  the 
rejection  of  any  sample  is  necessary  it  is  better  done  according 
to  judgment  exercised  there  than  at  the  works. 

Numbering  and  Mailing  Samples. — §  17.  The  samples  of 
residuum,  sand,  and  dust  should  be  numbered  consecutively, 
regardless  of  each  other  and  of  all  other  samples.  For  instance, 
the  first  sample  of  residuum  sent  for  analysis  would  be  No.  1,  the 
second  sample  No.  2,  and  so  on.  The  same  would  be  true  of  the 
sand  and  dust,  the  first  sample  of  each  of  these  materials  being 
No.  1  and  the  second  No.  2,  etc. 

Samples  of  surface  mixture  will  be  numbered  consecutively, 
but  in  case  two  samples  of  asphalt  cement  and  only  one  of  sur- 
face mixture  are  sent  on  the  same  day,  the  number  of  the  second 
sample  of  asphalt  cement  should  be  the  same  as  the  first,  but  a 
figure  "  2  "  should  be  placed  slightly  above  the  right-hand  upper 
corner  and  a  "  3  "  for  a  third  corresponding  to  .the  same  sample 
of  surface.  For  instance,  supposing  that  only  one  sample  of 
surface  mixture,  No.  10,  is  sent  on  one  day,  but  two  of  asphalt 
cement,  the  latter  would  be  numbered  10  and  102.  In  this  way 
the  A.  C.  sample  number  will  be  made  to  agree  with  that  of  the 
surface  mixture  in  which  it  was  used.  If  two  samples  of  surface 
mixture  and  two  of  asphalt  cement  are  sent  on  the  same  day 
the  numbers  on  each  should  correspond. 

It  must  be  insisted  upon  that  too  much  care  cannot  be  taken 
to  so  thoroughly  identify  samples  that  there  may  be  no  difficulty 
in  recognizing  their  origin  and  source,  even  after  the  lapse  of 
years.  The  habit  of  sending  materials  with  a  designation  by 
number,  or  otherwise  known  only  to  the  local  superintendent, 
must  be  discontinued. 

Samples  from  the  plant  should  be  mailed  at  once,  or,  if  hot, 
as  soon  as  cool,  and  usually  at  or  about  noon  of  the  day  on  which 
the  material  represented  by  the  samples  is  used.  It  may,  of 


518  THE  MODERN  ASPHALT  PAVEMENT. 

course,  be  necessary  to  mail  others  in  the  afternoon,  but  morn- 
ing samples  should  in  all  cases  be  sent  promptly  and  from  the 
nearest  letter-box  to  the  works.  The  practice  of  sending  samples 
to  the  superintendent's  office  should  be  discontinued.  Duplicate 
samples  can  be  sent  to  him  for  his  inspection  if  he  desires. 

In  order  to  check  delays  in  the  mails  and  in  other  ways  it 
is  well  to  mark  the  date  and  time  of  mailing  on  each  package,  and 
it  should  be  made  the  special  duty  of  some  one  person  to  attend 
to  this  matter,  and  he  should  be  held  responsible  for  mailing. 

A  new  series  of  sample  numbers  for  each  material  or  class  of 
materials  should  be  started  on  January  1  of  each  year. 


CHAPTER  XXVIII. 

METHODS  EMPLOYED  IN  THE  ASPHALT-PAVING  INDUSTRY 
FOR  THE  CHEMICAL  AND  PHYSICAL  EXAMINATION  OP 
THE  MATERIALS  OF  CONSTRUCTION. 

THE  results  of  the  examination  of  the  materials  in  use  in  the 
construction  of  asphalt  pavements  will  be  of  no  value  unless  the 
samples  or  specimens  representing  these  materials  are  collected 
with  great  care,  so  that  they  shall  be  truly  representative  of 
whatever  is  to  be  examined  The  directions  given  hi  the  preceding 
chapter  should,  therefore,  be  followed  in  taking  them. 

The  methods  practised  in  the  asphalt-paving  industry  in  judging 
the  different  materials  are  as  follows.  It  may  be  said  in  the  begin- 
ning that  these  methods  make  no  claim  to  great  analytical  accuracy, 
but  afford  that  information  needed  in  the  industry  with  a  maximum 
amount  of  accuracy  and  rapidity  at  a  minimum  expenditure  of 
time.  Many  of  them  are  only  of  relative  value;  that  is  to  say,  they 
do  not  furnish  absolute  data  and  can  only  be  used  when  some  well- 
known  specimen  of  the  same  material  is  treated  in  a  parallel 
manner  and  used  as  a  standard  of  comparison,  as  will  appear  later. 

Stone,  Gravel,  Slag,  etc. — These  materials,  which  form  the  coarser 
part  of  the  aggregate  in  the  foundation  and  the  entire  aggregate 
of  the  binder,  can  generally  be  examined  by  the  hand-and-eye 
method  without  submitting  them  to  laboratory  tests.  They  should 
be  free  from  adventitious  matter,  soil,  vegetable  debris,  etc.  They 
should  be  hard  and  when  shaken  together  or  passed  through  heating- 
drums  should  produce  but  a  small  amount  of  detritus.  If  necessary 
the  percentage  of  this,  formed  in  a  given  length  of  time  when  a 
definite  weight  of  the  material  is  revolved  in  a  rattler,  such  as  is 
used  in  testing  paving  bricks,  may  be  determined. 

519 


520  THE  MODERN  ASPHALT  PAVEMENT. 

For  binder,  stone  should  not  be  too  porous  and  tests  for  the 
amount  of  water  absorbed  in  twenty-four  hours  should  be  made. 

As  a  rule  the  examination  of  these  materials  for  use  in  the 
asphalt-paving  industry  is  in  no  respects  different  from  that  which 
would  be  made  were  they  to  be  used  for  other  purposes.  A  more 
elaborate  examination  of  any  stone  available  for  road  construction 
will  be  made  by  the  Office  of  Public  Roads,  U.  S.  Department 
of  Agriculture,  Washington,  D.  C.,  on  application  on  forms  sup- 
plied by  the  Department. 

Where  it  is  desirable  to  determine  the  proportions  of  stone  of 
different  sizes  which  go  to  make  up  the  aggregate  of  crushed  rock, 
as  in  arranging  the  grading  of  an  asphaltic  concrete,  this  can  be 
determined  by  means  of  riddles.  These  consist  of  perforated 
metal  set  in  circular  wooden  frames  sixteen  inches  in  diameter, 
with  circular  openings  of  the  following  diameter: 

1  inch,  J  inch,  J  inch,  f  inch  and  J  inch. 

Binder  Cement. — This  is  generally  examined  for  its  consistency 
alone  by  the  same  method  as  asphalt  cement  for  surface  mixture. 

Sand. — This  is  examined  as  to  the  material  of  which  the  grains 
are  composed,  their  shape,  the  character  of  their  surface,  the 
amount  of  silt,  clay,  loam,  coal,  or  vegetable  debris  it  contains, 
the  size  of  the  grains,  or  the  sand  grading  as  it  is  called,  and  the 
voids  in  the  sand  when  compacted.  The  grains  of  sand  are  more 
often  quartz  than  other  minerals.  At  times  some  limestone 
grains  or  shells  are  present  and  rarely  a  considerable  portion  of  the 
grains  are  silicates  of  igneous  and  volcanic  origin,  feldspar,  horn- 
blende, shales,  magnetite,  etc.,  as  at  Siboney  beach,  in  Cuba,  and 
in  Mexico.  At  Santiago  sands  derived  from  coral  reefs  occur. 
These  different  minerals  are  determined  in  the  usual  way  by  exam- 


METHODS  OF  ANALYSIS.  521 

ination  under  the  glass  and  with  reagents.  The  shape  of  the 
sand  grains  is  important  and  is  noted  with  a  glass.  It  may  be 
classed  as  sharp,  round,  medium,  irregular,  and  with  greater  detail 
as  to  special  peculiarities.  The  surface  of  the  grains  should  be 
examined  and  note  made  as  to  whether  it  is  smooth  and  polished, 
rough  like  ground  glass,  or  between  these  grades,  and  if  it  is  covered 
with  any  cementing  material  such  as  the  ferruginous  matter  adhering 
to  the  New  Jersey  sands.  The  capacity  of  the  surface  of  the  grains 
for  adsorbing  aqueous  vapor  may  also  be  determined  with  the 
object  of  learning  the  thickness  of  the  film  of  asphalt  cement 
which  it  will  probably  retain.  The  silt  or  clay  and  vegetable 
debris  are  detected  by  shaking  a  volume  of  30  cubic  centimeters 
of  sand  with  100  cubic  centimeters  of  water  in  a  graduated 
cylinder  until  thoroughly  wetted  and  allowing  the  coarse  particles 
to  subside.  A  rough  estimate  of  the  amount  of  silt,  etc.,  may  then 
be  made  by  the  eye.  The  separation  of  sands  into  grains  of  various 
sizes  by  the  use  of  sieves  is  the  most  important  means  of  determin- 
ing their  availability  for  paving  purposes.  Another  estimate  may 
be  reached  from  the  character  and  amount  of  material  passing  the 
finest  sieve  in  use  and  determining  the  size  of  the  grains. 

Determination  of  the  Grading  of  Sands. — This  is  done  with 
a  series  of  sieves  consisting  of  carefully  woven  brass  wire  cloth 
stretched  upon  a  tin  frame.  These  cloths  were  originally  so 
selected  that  the  average  diameter  of  the  particles  which  each  sieve 
passed  bore  some  definite  relation  to  those  passed  by  the  next 
finer  sieve.  The  average  diameter  of  these  particles  as  passed  by 
the  sieves  in  1908  and  the  names  given  in  the  trade  to  the  cloths 
are: 

200-mesh. . .  .085  millimeter 


100- 

173 

80- 

231 

50- 

377 

40- 

469 

30- 

595 

20- 

.  .  1  002 

10-  ' 

*  .            .  2.133 

The  200-mesh  cloth  was  selected  as  a  basis  of  measurement, 
being  the  finest  available  wire  cloth,  and  it  was  found  that  the 
average  diameter  of  the  largest  particles  it  will  pass  is  .085  mm. 


522 


THE  MODERN  ASPHALT  PAVEMENT. 


It  seemed  unnecessary  to  use  any  cloth,  such  as  the  150-mesh, 
between  this  and  the  100-mesh  sieve,  as  the  largest  particles  passed 
by  the  latter  were  only  twice  the  size  of  those  passed  by  the  former. 
For  the  same  reason  an  80-mesh  sieve  was  selected  for  the  third 
sieve,  as  its  largest  particles  were  more  nearly  three  times  the 
size  of  those  passed  by  the  200-mesh  sieve  than  any  other.  A 
50-mesh  sieve  passing  particles  about  four  times  as  great  in  diam- 
eter was  selected,  rejecting  the  use  of  the  60.  From  this  point 
the  increase  in  size  is  greater  at  each  step,  as  no  intermediate  sieves 
are  available  or  necessary.  The  particles  passing  the  40-,  30-, 
20-,  and  10-mesh  sieves  are  approximately  six,  eight,  twelve,  and 
twenty-four  times  the  diameter  of  the  finest  particles. 

Obtaining  satisfactory  sieves  of  this  description  is  not  readily 
accomplished.  Most  of  those  found  in  the  trade  are  made  of 
poorly  woven  cloth  or  the  cloth  is  so  stretched  in  putting  it  on 
the  frames  that  the  interstices  between  the  wires  are  much  altered 
in  size  and  no  two  sieves  of  the  same  number  will  agree.  It  is 
only  satisfactory,  therefore,  to  use  sieves  which  have  been  care- 
fully tested  and  compared  among  themselves  and  with  a  standard 
set,  or  to  determine  the  factor  for  correction  as  recommended  by 
Hazen.1 

Sieves  can  now  be  had  in  such  perfection  from  Howard  &  Morse, 
1197  DeKalb  Avenue,  Brooklyn,  N.  Y.,  that  a  sand  sifted  on 
one  set  of  sieves  in  Mexico  and  on  another  in  the  New  York  Test- 
ing Laboratory  by  different  operators  agreed  remarkably  well. 


Mexico. 

New  York 
Testing 
Laboratory. 

Passin 

g  200-mesh  

3% 

1% 

« 

100-         

6 

5 

1  1 

80-         

8 

7 

1  1 

50- 

35 

35 

n 

40-               ... 

25 

28 

ft 

30-         

13 

12 

(t 

20-         

7 

8 

tt 

10-         

3 
100 

4 
100 

Report  of  Mass.  State  Board  of  Health,  1892,  541. 


METHODS  OF  ANALYSIS. 


523 


The  finest  cloth,  in  the  200-mesh  sieve,  is  so  delicate  that  it 
must  be  used  with  care  and  continually  watched  to  detect  any 
deterioration.  Tearing  away  from  the  frame  is  a  frequent  occur- 
rence, but  such  a  defect  or  a  small  hole  in  the  cloth  can  be  stopped 
readily  with  soft  solder,  making  the  sieve  as  good  as  new.  New 
sieves  often  have  spots  of  solder  in  them  where  defects  due  to  imper- 
fect weaving  or  strains  in  mounting  the  cloth  have  been  stopped 
out. 

The  sieves  are  made  in  nests,  the  finest  being  of  the  largest 
diameter,  about  8  inches,  as  the  greatest  area  of  sifting  surface 


FIG.  30.— Sand  Scale. 


is  needed  with  this  cloth.  The  diameter  decreases  until  that 
of  the  10-mesh  sieve  is  only  5  inches.  For  storage  and  shipment 
the  sieves  thus  occupy  a  small  space. 

With  such  a  set  of  sieves  the  size  and  grading  of  the  particles 
of  a  sand  can  be  satisfactorily  determined  and  intelligently  expressed. 
The  operation  of  sifting  and  weighing  is  conducted  as  follows:  A 
definite  weight  of  sand,  50  grams,  is  taken.  This  is  weighed  out 
on  a  scoop  and  beam-scale  especially  constructed  for  use  in  making 
sand  siftings  and  sensible  to  half  a  gram,  Fig.  30.  It  is  the  ordi- 
nary No.  485  Fail-bank's  scale,1  supplied  to  seedmen  for  deter- 

1  Fairbanks  Co.,  New  York. 


524  THE    MODERN    ASPHALT   PAVEMENT. 

mining  the  dust  and  dirt  in  flaxseed,  modified  to  weigh  a  normal 
weight  of  50  grams  instead  of  1  pound.  The  50  grams  are 
divided  by  graduations  on  the  beam  of  this  balance  into  100  parts 
representing  per  cents,  thus  doing  away  with  any  calculations. 

The  sand  thus  weighed  out  is  thrown  upon  the  200-mesh  sieve. 
It  is  important,  however,  before  sifting  is  begun  that  the  cloth 
of  all  the  screens,  and  especially  the  three  finest,  be  thoroughly 
cleaned  with  a  stiff  bristle  brush  from  all  particles  which  may 
have  become  fixed  in  the  meshes.  For  this  purpose  a  small  stiff 
stencil  brush,  or  one  that  is  found  in  house-furnishing  stores 
for  scrubbing  porous  filters,  may  be  used.  After  rubbing  with  a 
brush  the  screen  is  struck  several  sharp  blows  up  and  down  to 
free  it  from  loose  particles. 

The  knack  of  using  the  sieves  satisfactorily  and  quickly  can 
hardly  be  described  in  print.  After  some  shaking  from  side  to  side, 
the  sieve  is  hit  sharply  on  the  table  orchard  surface  to  dislodge 
particles  which  have  filled  the  meshes  but  will  not  pass  through. 
Many  attempts  have  been  made  to  do  the  sifting  by  mechani- 
cal shaking  devices  and  with  sieves  of  all  sizes  at  one  time,  but 
with  little  success.  Where  a  large  number  of  siftings  is  required, 
hand  work  is  more  reliable  and  quicker. 

The  most  satisfactory  mechanical  device  we  have  found  is 
the  "Per  Se"  Tier  shaker,*  which  may  be  operated  by  power  or 
hand,  one  of  which  is  in  use  in  the  New  York  Testing  Laboratory 
for  screening  concrete  aggregates  or  when  large  quantities  of 
sand  must  be  considered. 

The  sifting  is  done  over  a  clean  piece  of  paper,  and  when  nothing 
passes  the  200-mesh  sieve,  all  lumps  of  loam  or  clay  which  readily 
break  up  under  the  fingers  having  been  rubbed  to  a  powder  on 
the  sieve  and  the  coarser  grains  cleaned  from  dust  by  attrition,  the 
residue  is  returned  to  the  scoop  of  the  balance. 

It  will  be  noticed  that  some  material  at  this  point  usually 
remains  in  the  meshes  of  the  wire  cloth.  This  is  allowed  to  remain 
there  when  the  residue  is  poured  from  the  sieve,  and  being  more 
nearly  the  size  of  the  grain  passed  by  this  sieve  than  the  next 
larger  is  included  with  the  200-mesh  or  the  coarser  mesh  sieves 
with  their  particular  size  grains  and  counted  as  passing  that  sieve. 
When  the  cloth  of  the  sieve  is  brushed  these  grains  are  rejected, 
and,  as  all  the  determinations  are  made  by  loss  and  not  by  direct 
weighing,  this  is  satisfactory. 

*  Howard  &  Morse,  Brooklyn,  N.  Y. 


METHODS   ol    ANALYSIS.  525 

The  per  cent  of  material  passing  the  200-mesh  sieve  is  arrived 
at  as  follows:  The  beam  at  the  point  where  the  poise  is  put  to 
weigh  out  the  original  50  grams  of  sand  is  graduated  zero,  and 
between  this  point  and  where  the  poise  balances  the  empty  scoop 
is  graduated  into  100  parts  which  may  be  read  as  per  cents.  The 
amount  of  material  which  has  been  passed  by  the  sieve  and  rejected 
may  then  be  seen  at  once  in  per  cents  on  weighing  the  residue  in 
the  scoop,  and  so  for  subsequent  sieves,  subtracting  of  course  each 
time  the  previous  reading  from  the  last. 

It  may  be  asked  why  the  200-mesh  sieve  is  used  first  and  why 
the  results  are  not  stated  in  per  cents  of  materials  retained  on 
the  different  sieves,  as  is  commonly  the  case.  One  of  the  reasons 
for  using  the  finest  sieve  first  is  that  if  the  dust  or  fine  material 
is  not  removed  at  once  much  of  it  is  blown  away  and  lost  in  the 
process  of  sifting.  As  in  this  method  the  percentages  are  deter- 
mined by  loss,  the  amount  disappearing  during  the  sifting  of  the 
200-mesh  sieve  first  is  of  no  consequence.  Another  is  that  the 
fine  material  adhering  to  the  coarser  grains  is  more  readily  separated 
from  them  by  attrition  in  the  finer  sieves,  and  that  the  presence  of 
the  coarser  sand  aids  in  breaking  up  lumps  and  expedites  sifting. 
In  fact  when  sifting  very  fine  material  like  dust  or  filler  it  is  usual 
to  place  some  coarse  gravel  not  passing  a  10-mesh  sieve, 
or  a  few  pennies,  on  the  200-mesh  to  aid  in  keeping  the  fine 
cloth  clear  and  to  break  up  lumps,  thus  doing  the  work  of  the  coarser 
particles  in  sand  or  mineral  aggregates  which  are  entirely  absent 
from  the  filler.  The  results  are  stated  in  per  cents  passing  a 
given  sieve  rather  than  that  retained,  because  this  results  in  making 
a  uniform  statement  and  not  some  figures  passed  and  some  retained, 
and  because  it  is  easier  to  associate  the  percentages  with  definite 
sized  particles  rather  than  with  sieves  which  will  not  pass  them. 

After  the  200-mesh  sieve,  the  others  are  used  in  order,  and  of 
course  more  rapidly  as  they  become  coarser.  The  greatest  care  is, 
of  course,  necessary  with  the  finest  sieve  to  clean  the  coarse  grains 
and  to  break  up  lumps  of  clay,  etc.,  for  which  the  finger  ends  are 
most  suited,  as  their  pressure  can  be  graduated  and  no  undue  force 
exerted  upon  the  cloth  or  upon  the  particles  which  do  not  readily 
disintegrate. 


526 


THE  MODERN  ASPHALT  PAVEMENT. 


The  actual  subtractions  made  in  a  sifting  appear  in  the  follow- 
ing facsimile  page  of  a  laboratory  record,  a  rubber  stamp  being 
a  decided  convenience  for  reporting  purposes: 

No.  30402 


100.0 


13 
4 


27 
13 


14 


57 

27 


30 


20 


11 


95 

88 


100 
95 


No.  30402 

Mesh 
No. 

Per  Cent. 
Passing. 

Bit. 

200 

4.0 

100 

9.0 

80 

14.0 

50 

30.0 

40 

20.0 

30 

11.0 

20 

7.0 

10 

5.0 

R.  10 

Total.  .  . 

100.0 

Remarks  : 

Voids  in  Sand  and  Mineral  Aggregates. — An  important  con- 
sideration in  connection  with  a  sand  or  mixture  of  sands  for  use  in 
asphalt  pavements  is  the  percentage  of  voids  which  it  contains 
on  compaction. 


METHODS  OF  ANALYSIS.  527 

The  ordinary  methods  of  determining  voids  by  measuring  the 
volume  of  water  that  must  be  added  to  the  compacted  mineral 
aggregate  to  fill  them,  or  pouring  the  compacted  aggregate  into  a 
measured  volume  of  water  in  a  graduate  and  noting  the  increase  of 
volume,  are  not  satisfactory,  because  in  the  first  way  it  is  difficult 
to  displace  all  the  air  in  the  voids  or  to  know  when  it  is  displaced ; 
in  the  second,  because  in  light  sand  and  sand  mixed  with  filler  a  cer- 
tain amount  of  the  fine  material  is  with  difficulty  persuaded  not  to 
float  or  leaves  at  best  a  meniscus  which  cannot  be  read. 

The  ordinary  means  of  attaining  ultimate  compaction  is  also 
deficient  in  accuracy.  At  air  temperatures  the  grains  of  any 
sand  or  dust  are  surrounded  by  a  film  of  adsorbed  aqueous  vapor 
which  prevents  their  packing  as  closely  as  possible.  To  attain 
satisfactory  compaction  the  aggregate  must  be  above  the  tempera- 
ture of  boiling  water.  It  is  necessary,  therefore,  to  use  hot  sand 
in  determining  the  voids  in  fine  materials  and  the  finer  the  ma- 
terial the  more  necessary  it  is. 

The  sand  aggregate  should  be  heated  to  about  250°  F.  in  a  small 
deep-form  iron  sand-bath1  and  then  compacted  in  one  of  the  fol- 
lowing ways. 

First  Method. — A  narrow-necked  flask,  graduated  to  100  c.c., 
is  filled  with  hot  sand,  the  neck  taken  in  one  hand  and  with  the 
other  hand  the  body  of  the  flask  is  struck  back  and  forth  from  the 
neck  to  the  bottom  with  a  peculiar  jarring  motion  with  a  wooden 
rod  of  about  £  of  an  inch  diameter  and  12  inches  long,  covered 
for  3  inches  with  a  piece  of  rubber  tubing.  The  jarring  settles 
the  sand  together  rapidly  in  the  flask  and  it  is  necessary  to  add 
more  from  tune  to  time.  When  jarring  ceases  to  compact  the  sand 
further  it  is,  after  having  been  brought  to  a  definite  volume,  emp- 
tied on  a  balance  and  weighed.  For  ordinary  purposes  this 
weight  divided  by  the  weight  of  an  equal  volume  of  quartz, 
will  give  the  actual  volume  the  particles  of  sand  occupy, 
and  from  the  difference  between  this  and  the  volume  of  the 
flask  the  voids  are  learned.  When  greater  accuracy  is  re- 
quired the  flask  with  the  hot  sand  must  be  allowed  to  cool  to 
ordinary  temperatures,  to  allow  for  contraction  of  the  quartz  in 

1  Eimer  &  Amend,  No.  4555,  6-inch. 


528  THE  MODERN  ASPHALT  PAVEMENT. 

volume,  and  again  filled  to  the  mark.  The  specific  gravity  of  the 
sand  grains  is  ordinarily  assumed  to  be  2.65,  but  it  may  vary,  and 
the  possibility  of  this  can  be  determined  at  a  glance.  When  this  is 
the  case  the  density  must  be  determined,  often  in  petroleum  or 
alcohol  when  fine  sand  is  present.  The  apparatus  designed  by 
D.  D.  Jackson,  which  has  been  described  by  him  in  a  paper  before 
the  Society  of  Chemical  Industry  in  1904,*  and  which  can  be 
obtained  from  Emil  Greiner  Co.,  45  Cliff  Street,  New  York  City, 
has  been  found  to  be  very  convenient  for  this  purpose. 

The  advantage  of  this  process  is  that  the  flask  is  filled  with  sand 
at  once  and  there  is  no  segregation  of  particles  of  different  sizes, 
especially  dust,  which  sometimes  takes  place  in  the  next  method. 

Second  Method. — The  hot  sand  is  taken  as  before,  but  it  is 
put  into  a  graduated  100  c.c.  cylinder,  10  c.c.  at  a  time,  and  com- 
pacted by  tamping  on  a  block  of  wood  after  each  addition.  When 
the  compaction  has  reached  its  ultimate  limit,  this  is  known  by 
a  disappearance,  especially  with  fine  material,  of  a  noise  due  to 
the  presence  of  an  air-cushion  between  the  particles  before  this 
point  is  reached.  Segregation  takes  place  to  a  limited  extent, 
especially  in  mixtures  of  sand  and  dust,  but  even  with  this  error 
a  greater  compaction  and  density  is  obtained  and  less  voids  are 
found  than  with  the  flask  method  for  the  same  aggregate,  the 
difference  being  about  1  per  cent  in  favor  of  the  cylinder. 

Volume  Weight  of  Sand. — From  the  weight  in  grams  of  100 
c.c.  of  a  sand  or  aggregate,  obtained  in  the  determination  of  the 
voids  as  just  described,  the  weight  per  cubic  foot  in  pounds  can  be 
found  by  multiplying  by  the  factor  .624.  This  is  of  value  in  deter- 
mining what  difference  in  the  weight  per  cent  of  bitumen  to  expect 
from  the  addition  of  the  same  volume  of  asphalt  cement  to  sands 
of  different  volume  weight. 

For  example,  an  aggregate  from  a  western  city  in  1899  weighed 
124.5  pounds  per  cubic  foot,  from  another  115.7.  It  is  very  easily 
seen  that,  with  the  same  volume  or  weight  of  asphalt  cement, 
added  to  each,  the  percentage  by  weight  in  an  ordinary  mixture 
will  be  much  lower  in  the  first  than  in  the  second  city,  and  in 

*  J.  Soc.  Chem.  Ind.  24,  593. 


METHODS    OF   ANALYSIS.  529 

practice  it  is  found  that  in  one  case  it  was  10  per  cent,  in  the  other 
11.3  per  cent.  This  determination  of  volume  weight  therefore 
serves  as  an  aid  to  our  interpretation  of  our  gravimetric  analysis. 

Dust  or  Filler. — A  dust  or  filler  of  ideal  quality  should  consist 
of  particles,  all  of  which  should  be  so  fine  that  they  will  pass  a 
200-mesh  screen.  Everything  coarser  merely  acts  as  sand.  It 
is  important,  too,  that  the  particles  should  be  much  finer  than 
a  size  that  will  merely  pass  this  sieve.  They  should  be  impal- 
pably  fine.  200-mesh  sand  is  not  the  same  as  dust  and  is,  in  fact, 
often  undesirable  in  a  surface  mixture. 

In  examining  a  dust  or  filler,  therefore,  it  is  necessary  to  deter- 
mine with  the  200-mesh  sieve  the  percentage  passing  it  and  to 
study  the  character  of  that  which  passes.  The  latter  examination 
can  be  made  in  two  ways.  As  we  have  no  sieve  available  for  the 
purpose  it  must  be  done  with  a  microscope  or  powerful  lens  which 
will  show  the  character  of  the  grains,  or  by  elutriation. 

Elutriation  Method. — Until  recently  the  only  means  of  deter- 
mining the  fineness  of  a  dust  or  filler  has  been  by  means  of  a 
200-mesh  sieve,  but  as  the  material  passing  this  sieve  might  con- 
sist in  whole  or  in  part  of  grains  as  large  as  .10  mm.  in  diameter 
which  can  hardly  be  considered  as  dust,  but  are,  on  the  contrary, 
only  fine  sand,  something  more  satisfactory  is  demanded.  This 
has  been  found  in  the  elutriation  process  in  use  in  soil  analysis. 
Five  grams  of  the  dust  to  be  examined  are  placed  in  a  beaker 
about  120  mm.  high,  holding  about  600  c.c.  The  beaker  is  nearly 
filled  with  distilled  water,  at  a  temperature  of  68°  F.,  and  agitated 
with  an  air-blast  until  the  dust  and  water  are  thoroughly  mixed. 
On  stopping  the  blast  the  liquid  is  allowed  to  stand  exactly  15 
seconds  and  the  water  above  the  sediment  immediately  decanted 
without  pouring  off  any  of  the  latter.  This  washing  is  repeated 
twice.  The  sediment  is  washed  out  into  a  dish,  dried,  and  weighed. 
The  loss  in  weight  represents  what  may  be  considered  as  dust  free 
from  sand.  The  washing  must  be  done  with  distilled  water,  since 
water  containing  salts  in  solution,  as  is  well  known,  induces  floc- 
culation.  This  method  can  also  be  used  with  hydraulic  cements, 
since  the  material  acted  upon  by  water  is  retained  in  suspension 
and  removed,  while  that  which  subsides  is  practically  unacted 


530  THE  MODERN  ASPHALT  PAVEMENT. 

upon  and  can  be  dried  and  weighed  without  difficulty.  The 
differentiation  in  this  case  can,  however,  not  be  carried  beyond 
that  resulting  in  15  seconds.  With  other  materials  the  differ- 
entiation of  the  particles  not  subsiding  in  15  seconds  can  be  carried 
further,  if  desired,  by  reagitating  the  decanted  material  and  allow- 
ing the  sedimentation  to  go  on  for  1  minute,  30  minutes,  1  hour, 
and  so  on.  The  preceding  method  is  an  adaptation  of  that  pro- 
posed by  Osborne  for  the  separation  of  the  particles  of  soil  of 
various  sizes,  for  further  details  of  which  reference  must  be  made 
to  the  Connecticut  Agricultural  Station  Annual  Report,  1886, 
page  141,  "  Principles  and  Practice  of  Agricultural  Analysis, 
Wiley,  Vol.  1,  page  196,  and  Hazen,  24th  Annual  Report  Mass. 
State  Board  of  Health,  1892,  page  543. 

Crude  Hard  Asphalts. — The  analysis  of  crude  asphalt  is  con- 
ducted in  much  the  same  way  as  that  of  the  refined  product  except 
that  it  is  necessary  to  determine,  in  the  former,  the  loss  of  water 
and  light  oil,  which  are  not  or  should  not  be  found  in  the  refined 
material.  If  there  is  any  question  as  to  the  dryness  of  the  refined 
material  this  should,  of  course,  be  first  determined  in  the  same 
manner  as  with  the  crude.  The  determination  of  water  can  be 
made  in  two  ways. 

Ordinary  Method. — Ordinarily  it  is  sufficiently  accurate  to 
weigh  out  2  to  5  grams  of  the  material  in  a  crucible,  or  preferably 
on  a  watch  glass  to  expose  more  surface,  and  to  subject  it  to  a 
temperature  of  100°  C.,  in  a  well  regulated  air-bath  with  the  pre- 
cautions described  on  pp.  534, 535,  until  it  ceases  to  lose  in  weight  to 
an  extent  of  more  than  .2  to  .3  per  cent  on  successive  heating. 
A  greater  concordance  is  not  sought,  as  many  asphalts  continue  to 
lose  light  oils  gradually  at  this  temperature.  The  oven  which 
is  used  for  this  purpose  in  the  author's  laboratory  is  one  of  the 
Lothar-Meyer  form,  or  a  modification  of  this,  which  is  fully  described 
on  page  536,  Figs.  31  and  32.  The  degree  of  fineness  to  which  the 
crude  asphalt  should  be  reduced  before  weighing  out  is  dependent 
upon  the  amount  of  water  it  contains.  In  powdering  some  asphalt, 
such  as  crude  Trinidad,  the  material,  since  it  contains  29  per  cent 
of  water  in  emulsion  with  bitumen,  begins  to  lose  water  at  once. 
It  can,  therefore,  only  be  broken  into  coarse  lumps  and  not  reduced 


METHODS    OF    ANALYSIS.  531 

to  a  powder  until  after  a  preliminary  determination  of  the  water 
thus  lost  by  the  coarse  material.  Other  asphalts,  containing  only 
a  small  amount  of  hygroscopic  or  adventitious  water,  may  be 
ground  up  at  once,  while  some  which  are  not  readily  powdered 
may  be  cut  into  small  pieces.  If  it  is  necessary  to  determine  the 
water  absolutely  it  may  be  absorbed  and  weighed  and  the  difference 
stated  as  gas  or  light  hydrocarbons.  This  is  hardly  necessary  from 
a  technical  point  of  view. 

Alternate  Method. — For  asphalts  such  as  crude  Trinidad,  in 
which  the  difficulties  described  above  are  met,  a  different  method 
of  procedure  is  advisable.  The  substance  is  very  quickly  reduced 
to  a  coarse  powder  only,  in  a  mortar  provided  with  a  cover,  through 
which  the  pestle  passes.  Five  grams  of  it  are  spread  out  on  a 
4-inch  watch-glass,  and  this  is  placed  in  vacuo  over  sulphuric 
acid  for  twelve  hours  and  the  loss  determined.  It  should  then 
be  reground  to  a  fine  powder  and  exposed  again  in  vacuo  until 
it  ceases  to  lose  weight.  The  loss  may  be  stated  as  water. 

In  the  examination  of  a  cargo  of  crude  Trinidad  for  technical 
purposes,  about  50  grams  in  small  lumps  are  placed  in  a  flat  8-oz. 
oblong  tin  box  and  dried  to  practically  constant  weight  at  325°  F. 
The  results  thus  obtained  are  comparable  with  those  obtained 
in  the  refining  by  steam  at  this  temperature. 

In  whichever  way  the  asphalt  is  dried  a  sufficient  quantity  is 
prepared  and  preserved  in  this  condition  in  a  tightly  stoppered 
bottle,  for  analysis.  Asphalts  which  cannot  be  reduced  to  powder 
are  used  in  mass.  The  powdered  asphalts  have  a  slight  tendency 
to  absorb  hygroscopic  moisture  and  must  be  protected  from  the 
air. 

In  the  dried  condition  crude  asphalts  can  be  considered,  as 
far  as  analysis  is  concerned,  simply  as  refined  material,  and  all 
determinations  should  be  done  with  and  percentages  calculated  to 
this  material,  including  the  water  or  loss,  by  calculation,  in  the 
final  results  if  desired. 

Refined  Asphalts. — Examination  of  refined  asphalts  in  their 
most  extended  form  include  determinations  given  on  the  accompany- 
ing form,  used  as  a  convenience  in  reporting.  With  well-known 
asphalts  but  a  limited  number  of  determinations  are  necessary  for 


532  THE  MODERN  ASPHALT  PAVEMENT. 

the  purpose  of  detecting  the  lack  of  uniformity  or  peculiarities  in 
the  material. 

NEW  YORK  TESTING  LABORATORY. 

Test  number MAURER,  N  J 

Source  of  supply 


PHYSICAL  PROPERTIES. 
Specific  gravity,  78°  F./780  F.  original  substance,  dry. 

"  "  "  pure  bitumen 

Color  of  powder  or  streak 

Lustre 

Structure 

Fracture 

Hardness,  original  substance " 

Odor 

Softens 

Flows 

Penetration  at  78°  F 


CHEMICAL  CHARACTERISTICS. 
Original  substance: 

Loss,  212°  F.,  1  hour 

Dry  substance: 

Loss,  325°  F.,  7  hours 

Character  of  residue 

Penetration  of  residue  at  78°  F 

Loss,  400°  F.,  7  hours  (fresh  sample) 

Character  of  residue 

Penetration  of  residue  at  78°  F. . . 


Bitumen  soluble  in  CS2,  air  temperature. 

Inorganic  or  mineral  matter 

Difference.  . 


Malthenes : 

Bitumen  soluble  in  88°  naphtha,  air  temperature.. . . 

This  is  per  cent  of  total  bitumen 

Per  cent  of  soluble  bitumen  removed  by  H2SO4 

Per  cent  of  total  bitumen  as  saturated  hydrocarbons. 


Bitumen  soluble  in  62°  naphtha. 
This  is  per  cent  of  total  bitumen. 


METHODS   OF    ANALYSIS.  533 

Carbenes: 

Bitumen  insoluble  in  carbon  tetrachloride,  air  temperature. 
Bitumen  more  soluble  in  carbon  tetrachloride,  air  tem- 
perature   

Bitumen  yields  on  ignition: 

Fixed  carbon.  .  


Sulphur 

Ultimate  composition B 

Remarks: 

Physical  Properties. — Specific  Gravity. — The  specific  gravity 
of  the  dried  asphalt  is  taken  in  a  picnometer  at  25°  C.  and  referred 
to  water  at  the  same  temperature.  This  temperature  has  been 
selected  as  the  most  convenient  mean  between  the  room  tem- 
peratures of  winter  and  summer,  and  is  much  more  suitable  in 
our  surroundings  than  the  lower  temperature  generally  in  use 
abroad,  15°  C.  Determinations  at  the  latter  temperature  are 
much  hampered  by  the  great  difference  between  it  and  OUT  labora- 
tory temperatures,  the  rapid  expansion  after  cooling  to  15°  C. 
being  difficult  to  provide  for,  as  well  as  the  condensation  of  mois- 
ture on  the  surface  of  the  picnometer  when  the  dew  point  is  high, 
a  room  with  the  temperature  in  use  for  penetrations  is  always 
available  for  density  and  other  temperature  work.  This  tem- 
perature of  78°  F.  has  therefore  been  taken  as  a  normal  one  for 
all  physical  work  on  asphalts.  The  specific  gravity  of  the  pure 
bitumen  extracted  from  those  asphalts  carrying  a  considerable 
amount  of  mineral  matter,  in  a  way  to  be  subsequently  described, 
is  also  determined  in  the  same  way. 

The  usual  determination  of  the  outward  physical  features  of 
any  mineral  substance,  Color  of  Streak,  Structure,  Fracture,  Hard- 
ness, and  Odor  if  any,  are  noted. 

The  color  of  the  streak  or  of  the  powder  of  a  hard  asphalt  is 
in  certain  cases  characteristic.  For  example,  in  the  case  of  refined 
Trinidad  lake  asphalt  the  powder  is  a  bluish-black  color,  while 
that  of  the  refined  Trinidad  land  asphalt  is  much  browner.  Pow- 


534  THE  MODERN  ASPHALT  PAVEMENT. 

dered  gilsonite  is  of  a  very  light-brown  color.  Powdered  gra- 
hamite  is  quite  black. 

The  structure  of  a  solid  native  bitumen  may  be  either  homo- 
geneous or  it  may  show  the  presence  of  cavities  containing  gas, 
particles  of  adventitious  mineral  matter,  shale  or  clay,  or  other 
peculiarities. 

The  fracture  may  be,  in  the  case  of  very  pure  bitumens,  con- 
choidal  or  semi-conchoidal,  pencillated  or  hackley  in  the  case  of 
grahamite,  or  irregular. 

The  hardness  of  the  original  material,  if  it  contains  much 
mineral  matter,  may  be  stated  in  degrees  of  Mohrs  scale,  that 
of  the  pure  bitumen  in  several  ways.  It  is  either  brittle,  like 
glance  pitch,  or  soft  enough  to  be  penetrated  with  the  needle  of 
a  penetration  machine  in  which  case  the  hardness  is  expressed 
in  degrees  of  this  machine. 

The  odor  in  the  case  of  many  bitumens  is  characteristic.  That 
from  Venezuelan  asphalt,  found  near  the  Gulf  of  Maracaibo,  is 
extremely  strong  and  rank,  while  others  are  more  purely  asphaltic, 
especially  on  warming.  The  heat  in  any  case  brings  out  the 
odor  to  a  degree  not  observed  in  the  cold  material. 

Loss  on  Heating. — It  is  sometimes  necessary  to  determine 
the  loss  which  an  asphalt  suffers  on  heating  for  a  time  to  definite 
temperatures.  The  length  of  time  has  been  arbitrarily  taken 
as  seven  hours  and  the  temperature  325°  F.  and  400°  F. 

The  determination  is  made  as  follows:  In  a  No.  1  crystallizing- 
dish,  2J  inches  in  diameter  and  1T\  inches  high,  or  3  oz.  deep  seam- 
less tin  box  of  this  size,1  are  placed  20  grams  of  the  material 
under  examination.  The  exact  dimensions  of  the  dish  are  of  no 
great  importance,  as  can  be  seen  from  the  following  determina- 
tions: 

1  American  Can  Co.,  New  York. 


METHODS   OF    ANALYSIS 


535 


TWENTY  GRAMS  OF  RESIDUUM  AT  325°  F.  FOR  SEVEN  HOURS. 


1 

2 

3 

Weight  of  dish         

23.3465 

18.1825 

19.1855 

1.51" 

1.47" 

1.28" 

2.15" 

2.15" 

2.20" 

.06 

.045 

.05 

.925 

.920 

.950 

Position  in  b&th.  •••  

Left 

Right 

Middle 

Should  it  be  necessary  to  use  a  very  much  larger  dish  the 
weight  of  the  material  to  be  taken  should  be  calculated  so  that 
the  volume  which  it  holds  shall  bear  the  same  relation  to  the 
surface  exposed  as  in  the  case  of  the  smaller  dish.  It  is  necessary 
to  take  separate  portions  of  the  substance  for  each  determination, 
and  not  to  attempt  to  determine  the  loss  at  400°  F.  from  the 
sample  which  has  been  previously  heated  at  325°  F. 

The  dish  is  heated  to  the  requisite  temperature  for  the  given 
length  of  time  in  an  oven  the  temperature  of  which  is  uniform  in 
all  parts,  something  that  is  not  as  easily  accomplished  as  might 
be  supposed,  and  with  the  assurance  that  the  materials  are  main- 
tained at  the  proper  temperature,  a  temperature  which  it  has 
been  found  is  not  indicated  by  that  recorded  by  a  thermometer, 
that  registers  merely  the  temperature  of  the  air  in  the  bath.  Such 
an  oven  is  not  only  difficult  to  obtain,  but  the  manner  in  which 
the  best  form  is  used  is  of  great  importance. 

Farm  of  Oven  Employed  in  the  Author's  Laboratory. — Extended 
experience  with  various  ovens  thoroughly  convinced  the  author 
that  none  of  the  forms  ordinarily  furnished  by  the  supply  dealers 
were  satisfactory,  especially  if  they  are  heated  by  the  direct  appli- 
cation of  the  flame  to  the  bottom  of  the  oven.  The  air-bath  of 
Lothar-Meyer l  was  found  to  be  by  far  the  best,  but  inconvenient, 


1  Berichte,  1889,  22,  1,  879. 


536 


THE    MODERN    ASPHALT    PAVEMENT. 


owing  to  the  fact  that  the  interior  is  not  readily  reached.  On  this 
account  an  oven  has  been  designed,  possessing  all  the  advantages 
of  Meyer's  form,  but  much  more  convenient  for  use  in  an  asphalt 
laboratory.  The  accompanying  illustrations  show  its  construc- 
tion, Figs.  31  and  32. 


FIG.  31. — New  York  Testing  Laboratory  Oven. 


It  will  be  seen  that  the  bath  instead  of  being  heated  from  the 
bottom  is  heated  by  a  10-inch  ring  burner  immediately  under- 
neath the  space  between  the  oven  itself  and  the  outside  wall,  as 
in  the  Lothar-Meyer  form.  The  perforations  in  this  ring  are  neces- 
sarily systematically  spaced  to  allow  for  the  greater  gas  pressure  at 


METHODS    OF   ANALYSIS.  537 

the  point  where  the  latter  enters,  in  order  that  a  uniform  amount  of 


ii  n  \  i   rm 


FIG.  32. — New  York  Testing  Laboratory  Oven. 

heat  may  be  furnished  at  all -points  in  the  circumference.  If  this 
is  properly  arranged,  and  the  inner  chamber  of  the  bath  is  well 
made,  no  further  precautions  are  necessary  to  avoid  inequalities  of 
temperature  caused  by  the  direct  entrance  of  hot  air  from  the  burner 
into  the  oven.  In  standardizing  the  bath  it  is  necessary  that  a 
number  of  thermometers  should  be  inserted  at  different  points  in 
order  to  determine  that  the  temperature  at  all  points  is  uniform. 
If  this  is  not  the  case  the  openings  in  the  ring  burner  must  be 
rearranged  until  this  is  accomplished.  The  interior  of  the  bath,  it 
will  be  noticed,  is  provided  with  a  fan  for  causing  a  circulation  of 
air  to  bring  about  still  greater  uniformity,  this  fan  being  moved  by 
any  convenient  source  of  power. 

The  inner  chamber  is  provided  with  a  perforated  shelf  of  metal. 
The  dishes  containing  the  material  to  be  subjected  to  the  desired 
temperature,  it  has  been  found,  cannot  be  placed  directly  on  this 


538  THE  MODERN  ASPHALT  PAVEMENT. 

shelf  with  the  assumption  that  they  will  not  exceed  the  tempera- 
ture recorded  by  the  thermometers  in  the  air  circulating  in  the 
bath.  The  conductivity  of  the  metal  shelf  is'  so  much  greater  than 
that  of  the  air  that  the  dishes  will  attain  a  much  higher  temperature 
than  the  air  in  the  bath.  This  difficulty  can  be  avoided  to  a  very 
considerable  extent  by  placing  a  sheet  of  asbestos  over  the  shelf; 
but  even  then  the  temperature  of  the  material  in  the  dish  will  be 
somewhat  different  from  that  of  the  air  in  the  bath.  In  order  to  de- 
termine what  the  temperature  of  the  former  is  it  has  been  found  nec- 
essary to  use  a  thermometer,  which  is  immersed  in  heavy  residuum 
oil  placed  alongside  the  material  under  examination.  The  reading 
of  this  thermometer  will  give  the  temperature  to  which  the  material 
under  examination  is  being  subjected.  The  thermometer  exposed 
only  to  the  air  of  the  bath  is  then  observed  merely  for  the  purpose 
of  detecting  any  sudden  changes. 

It  will  be  noted  that  the  cover  to  this  bath  is  hinged  so  that  it 
may  be  opened  conveniently  for  inserting  and  removing  the  dishes 
containing  the  material  under  examination.  It  is  provided  with 
numerous  openings  for  the  insertion  of  thermometers  and  a  gas 
regulator,  and  for  the  escape  of  the  vapor  of  hydrocarbons  which 
have  been  volatilized.  The  outer  shell  of  the  bath  is  covered 
with  asbestos  for  insulating  purposes.1 

Melting  or  Flowing  Point. — The  solid  native  bitumens  can 
have  no  definite  melting  point,  for  the  reason  that  they  are  com- 
posed of  mixtures  of  hydrocarbons.  It  is  only  possible,  therefore, 
to  determine  rather  arbitrarily  the  point  at  which  the  material 
softens  or  flows,  and  with  special  reference  to  the  relation  of  this 
point  toward  some  standard  bitumen.  This  is  determined  as 
follows: 

A  crystallizing  dish,  about  2^  inches  in  diameter  and  with  1^ 
inch  sides,  filled  with  clean  mercury  to  a  distance  of  J  inch  from 
the  top,  is  placed  over  a  20-mesh  wire  gauze  and  heated  by  a 
small  flame  protected  from  draughts  by  a  chimney.  On  the  sur- 
face of  the  mercury  is  placed  a  thin  microscopic  cover-glass, 
No.  2-0,  carrying  the  specimen  of  asphalt  under  examination. 

1  The  bath  is  constructed  for  the  author  by  the  Hauck-Seebach  Co.,  291 
Essex  Street,  Brooklyn,  N.  Y. 


METHODS    OF    ANALYSIS. 


539 


When  dealing  with  hard  asphalts  that  can  be  ground  rather 
coarsely,  several  fragments  which  will  pass  a  40-mesh  sieve  and 
be  retained  on  a  50-mesh  sieve  (about  .50  mm.  diameter)  are 
spread  on  the  cover  glass  and  placed  upon  the  surface  of  the 


FIG.  33 

mercury,  covered  with  a  funnel,  from  which  the  stem  has  been 
cut  and  the  thermometer  passed  through  the  orifice  until  the 
bulb  is  immersed  in  the  mercury.  It  is  held  in  position  by  a 
clamp  attached  to  the  ring-stand  holding  the  dish.  Under  the 
dish  a  burner  is  placed  that  can  be  regulated  to  a  small  flame  and 


540  THE    MODERN    ASPHALT  PAVEMENT. 

heat,  so  that  the  rise  of  temperature  will  be  from  three  to  five 
degrees  per  minute.  In  a  short  time  it  will  be  noticed  that  the 
specimens  will  have  changed  from  the  brown  or  brownish-black 
color  of  the  powder  to  that  more  nearly  approaching  tlie  original, 
with  a  slight  rounding  of  the  individual  grains.  On  further  heat- 
ing these  globules  flow  together  and  form  a  thin  sheet  on  the  glass. 
The  point  at  which  the  specimen  begins  to  flow,  as  indicated  by 
the  thermometer,  is  noted  as  the  melting  or  flowing  point. 

Asphalts  that  cannot  be  ground  are  softened  and  pulled  out 
to  a  thread  and  cut  into  small  pieces,  about  1  cubic  mm.  Sev- 
eral pieces  should  be  placed  on  the  glass  together,  as  one  will 
serve  as  a  check  on  the  other,  and  thereby  lessen  the  chance  of 
error.  The  softening  point  may  be  noted  by  the  rounding  of 
the  particles  and  the  beginning  of  the  flow,  or  when  the  specimen 
begins  to  spread  out,  which  is  always  at  the  point  of  contact  with 
the  cover-glass,  is  set  down  as  the  flowing  point  or  the  tempera- 
ture at  which  the  specimen  will  melt. 

Determination  of  Total  Bitumen. — One  gram  of  the  dried 
or  refined  material,  in  a  state  of  very  fine  powder,  if  possible,  is 
weighed  out  and  introduced  into  a  200  c.c.  Erlenmeyer  flask  of 
Jena  glass  and  covered  with  about  100  c.c.  of  bisulphide  of  carbon. 
It  is  then  set  aside  for  at  least  five  hours,  or  overnight,  at  the  tem- 
perature of  the  laboratory.  In  the  meantime  a  Gooch  crucible 
is  prepared  with  an  asbestos  felt  and  weighed.  This  Gooch 
crucible  is  of  special  form  with  a  large  filtering  surface.  It  holds 
30  c.c.,  is  4.4  cm.  wide  at  the  top,  tapering  to  3.6  cm.  at  the 
bottom  and  2.6  cm.  deep.  This  is  much  better  for  percolation  work 
than  the  usual  narrow  form  of  Gooch.  The  felt  is  made  by  beating1 
up  long-fibre  Italian  asbestos  in  a  mortar,  and  suspending  the  finei 
particles  in  water  and  quickly  pouring  off  from  the  coarse  particles. 
Too  much  of  the  latter  should  not  be  removed,  or  the  felt  will  be 
too  dense.  The  decanted  asbestos  and  water  can  be  kept  in  a 
bottle  for  use.  To  prepare  the  felt  the  asbestos  and  water  are 
shaken  up  and  what  is  found  to  be  a  proper  amount  poured  into 
the  crucible,  which  has  in  the  meantime  been  attached  to  a  vacuum 
filtering-flask  by  the  proper  glass  and  rubber  connections.  As 
soon  as  the  asbestos  has  somewhat  settled  the  vacuum-pump  is 


METHODS    OF    ANALYSIS.  541 

started  and  the  felt  firmly  drawn  on  the  bottom  of  the  crucible. 
It  is  then  dried,  ignited,  and  weighed. 

After  standing  a  proper  time  the  bisulphide  is  decanted  very 
carefully  upon  the  filter  which  is  supported  in  the  neck  of  a  wide- 
mouth  flask  and  allowed  to  run  through  without  pressure.  The 
flask  after  being  tipped  to  pour  the  first  portion  is  not  again  placed 
erect  in  order  to  avoid  stirring  up  the  insoluble  material,  but  is 
held  at  an  angle  on  any  suitable  base,  such  as  a  clay  chimney. 
After  all  the  bisulphide  has  been  decanted  more  is  added  and 
the  insoluble  matter  shaken  up  with  it.  This  is  allowed  to  settle 
and  decanted  as  before,  the  insoluble  matter  being  finally  brought 
on  the  filter  and  washed  with  the  solvent  until  clean.  The  excess 
of  bisulphide  is  allowed  to  evaporate  from  the  Gooch  crucible 
at  the  temperature  of  the  room.  It  is  then  dried  for  a  short  time 
at  100°  C.  and  weighed.  The  loss  of  weight  is  the  percentage  of 
bitumen  soluble  in  €82- 

In  the  meantime,  however,  the  bisulphide  which  has  passed 
the  filter  is  allowed  to  subside  for  twenty-four  hours,  if  possible, 
and  is  then  decanted  carefully  from  the  flask  in  which  it  has  been 
received  into  a  weighed  platinum  or  unweighed  porcelain  dish. 
If  there  is  any  sediment  in  this  flask  it  must  be  rinsed  back  into 
the  Gooch  crucible  with  bisulphide  and  the  crucible  again  washed 
clean.  The  solvent  in  the  dish  is  placed  in  a  good  draught  and 
lighted.  When  all  the  bisulphide  has  burned,  the  bitumen 
remaining  in  the  dish  is  burned  off  over  a  lamp  and  the  mineral 
residue,  which  was  too  fine  to  subside,  is  weighed,  if  the  burning 
was  done  in  a  platinum  dish,  or  dusted  out  and  added  to  the  cru- 
cible if  in  a  porcelain  one.  In  the  former  case  the  weight  is  added 
to  that  of  the  Gooch  crucible  or  subtracted  from  the  per  cent 
of  bitumen,  found  without  its  consideration,  as  a  correction. 
Care  must  be  used  in  this  method  of  procedure  that  the  solvent 
does  not  creep  over  the  sides  of  the  crucible  and  that  the  outside 
is  free  from  bitumen  before  weighing.  In  order  to  avoid  this  the 
crucible  is  supported  in  the  neck  of  a  flask  with  three  constrictions, 
the  neck  extending  above  the  top  of  the  crucible  and  the  latter 
being  covered  with  a  watch-glass.  These  flasks  are  made  for 


542  THE  MODERN  ASPHALT    PAVEMENT. 

the  author  by  E.  Machlett  &  Son,  143  East  Twenty-third  Street, 
New  York. 

Mineral  Matter  or  Ash. — One  gram  of  the  same  sample  of 
material  used  for  the  determination  of  bitumen  is  weighed  out  in  a 
No.  0  Royal  Berlin  porcelain  crucible  and  burned  in  a  muffle  or 
over  a  flame  until  free  from  carbon.  This  must  be  determined 
by  breaking  up  the  cake  of  ash,  moistening  with  water  or  alcohol, 
and  observing  if  any  black  particles  of  coke  are  present.  The 
weight  of  the  residue  is  stated  as  inorganic  or  mineral  matter. 

The  determination  is  of  course  not  exact,  sulphuric  acid  and 
the  alkalies  being  volatilized  in  many  cases,  but  it  is  satisfactory 
for  technical  purposes. 

Naphtha  Soluble  Bitumen. — For  the  purpose  of  determining  the 
percentage  of  bitumen  soluble  in  naphtha  distillates,  88°  and  62°  B. 
are  used.  It  is  extremely  important  that  these  naphthas  should  be 
of  the  exact  degree  specified,  since  differences  in  density  will  make 
an  appreciable  difference  in  the  amount  of  bitumen  extracted. 
The  distillate  should  be  that  obtained  from  a  paraffine  petroleum. 
The  density  of  each  lot  should  be  carefully  determined  with  a 
Westphal  balance  at  60°  F.  and  if  it  is  too  dense  or  too  light,  it 
can  be  brought  to  the  proper  density  by  diluting  with  a  heavier 
or  lighter  naphtha  as  required.  Redistillation  of  these  naphthas  is 
unnecessary  as  the  products  of  distillation  are  no  more  uniform 
than  the  original  naphtha. 

It  will  be  found  very  necessary  that  hard  bitumens  should  be 
reduced  to  an  impalpable  powder  before  attempting  to  extract 
them,  as  otherwise  the  extraction  will  not  be  complete.  The  softer 
bitumens  should  be  divided  as  much  as  possible. 

The  bitumen  is  usually  extracted  with  naphthas  of  both  densi- 
ties hi  order  to  determine  the  difference  in  their  action.  If  the 
amount  extracted  by  each  is  the  same  or  nearly  the  same  it  will  point 
to  the  fact  that  the  bitumen  consists  of  hard  asphaltenes  mixed  with 
light  malthenes,  the  latter  equally  soluble  in  naphtha  of  both 
degrees  of  density,  and  but  little  intermediate  hydrocarbons,  or  of 
the  very  hard  asphalts  fluxed  artificially  with  some  light  oil. 
If,  on  the  other  hand,  there  is  a  very  considerable  increase  in  the 
percentage  dissolved  by  the  62°  over  the  88°  naphtha  it  may  be 


METHODS  OF  ANALYSIS. 


543 


assumed  that  the  malthenes  are  well  graded  and  natural  constitu- 
ents of  the  bitumen  which  is  being  examined.  In  certain  cases, 
however,  the  use  of  the  two  naphthas  is  unnecessary.  It  would  be 
useless  to  extract  a  maltha  with  a  dense  naphtha  or  glance  pitch 
or  albertite  with  a  lighter  one. 

In  determining  the  naphtha  soluble  bitumen  in  asphalts  and 
other  hydrocarbons  it  was  the  custom  from  1887  to  1899  to  make 
the  extractions  in  small  beakers,  No.  0.     One  gram  of  the  substance 
was  weighed  out  and  covered  with  a  sufficient  amount  of  naphtha, 
about  75  c.c.,  and  placed  on  the  steam  bath  and  allowed  to  boil 
until   the   solvent   became   thoroughly   saturated.     It   was   then 
decanted  through  a  weighed  Gooch  crucible  and  the  residue  succes- 
sively treated  until  free  from  bitumen  soluble  in  naphtha.     As  it 
was  almost  impossible  to  get  concordant  results  in  this  way,  on 
account  of  the  loss  of  the  lighter  constituents  of  the  naphtha  and 
the  consequent  increase  of  density  of  the  solvent,  resort  was  had 
to  the  use  of  Erlenmeyer  flasks,  about  12  cm.  high  and  200  c.c. 
capacity.     One  gram  of  the  substance  was  weighed  out  and  boiled 
with  the  naphtha  in  a  loosely  stoppered  flask  for  from  one-half 
to  one  hour,  according  to  the  character  of  the  material  to  be  ex- 
tracted.   The  solution  was  decanted  as  with  the  beaker  method 
and  the  treatment  repeated.     The  results  were  a  slight  improve- 
ment over  the  open  beaker,  but  not  entirely  satisfactory.     The  use 
of  a  return  cooler  was  then  tried  and  gave  good  results  with  62° 
naphtha,  but  as  the  loss  of  light  hydrocarbons  from  the  88°  naphtha 
could  not  be  controlled,  even  in  this  way,  any  heating  with  this 
very  volatile  solvent  was  abandoned.     The  change  in  the  two  grades 
of  naphtha  on  heating  are  shown  from  the  following  experiments: 

EFFECT   OF  HEATING  NAPHTHA  AS  IF  USED   AS  A  SOLVENT. 


Degrees  B. 

Gravity 
15°  C./150  C. 

Treatment. 

Loss  by 
Weight, 
Per  Cent. 

Loss  by 
Volume, 
Per  Cent. 

Residue, 
Specific 
Gravity. 

88° 
«  < 

(i 

0.6379 
0.6379 
0.6379 

Return  cooler 

i  (           (  t 

Open  flask 

51.2 
65.6 

53.5 

40.0 

37.0 
48.0 

0.6523 
0.6523 
0.6585 

62° 

u 

0.7321 
0.7321 

Return  cooler 
Open  flask 

3.0 
10.0 

1.0 
3.0 

0.7352 
0.7393 

544  THE   MODERN   ASPHALT    PAVEMENT. 

It  appears,  therefore,  that  heating  increases  the  density  of  both 
naphthas,  and  consequently  their  solvent  powers,  from  inability 
to  condense  the  more  volatile  parts,  but  that  the  change  in  the  62° 
naphtha  is  small,  so  that  it  can  be  safely  heated  to  a  slight  extent. 

As  a  result  of  these  experiments  all  determinations  are  now 
made  with  cold  naphtha  by  the  following  method: 

One  gram  of  the  substance  is  weighed  into  a  200  c.c.  Erlenmeyer 
flask,  covered  with  naphtha  and  allowed  to  stand,  as  in  estimating 
total  bitumen,  in  fact  the  entire  process  is  the  same  with  the  ex- 
ception that  one  or  two  precautions  must  be  observed.  It  is  well 
not  to  attempt  to  break  up  any  lumps  with  a  stirring  rod,  as  the  sub- 
stance, especially  the  softer  asphalts,  may  then  adhere  to  the  rod 
or  flask  and  be  difficult  to  detach.  It  may  also  be  necessary  to 
treat  the  substance  with  several  portions  of  the  solvent  instead 
of  with  two  or  three,  as  in  the  case  of  carbon  disulphide.  No  heat 
is  applied  at  any  time  in  the  process. 

The  naphtha  soluble  bitumens  are  frequently  denominated 
petrolenes.  The  writer  has  recently  suggested  the  name  malthenes 
as  bitumen  of  this  nature  closely  resembles  maltha  in  its  consis- 
tency. Objection  has  been  raised  by  partisans  to  the  use  of  the 
name  petrolene  as  leading  to  the  conclusion  that  petrolene  is  a  defi- 
nite compound.  Of  course  it  is  no  more  a  definite  compound  than 
kerosene,  but  a  mixture  of  various  hydrocarbons  like  the  latter. 
The  objection  to  this  designation  must,  therefore,  fall  to  the  ground, 
although  petrolenes  or  malthenes  may  be  more  satisfactory  as  being 
less  misleading. 

Determination  of  the  Character  of  the  Malthenes  or  Naphtha 
Soluble  Bitumens. — The  determination  of  the  relative  proportion 
of  saturated  and  unsaturated  hydrocarbons  which  constitute  the 
malthenes  is  very  important  in  differentiating  the  solid  bitumens. 
It  is  made  as  follows: 

The  88°  naphtha  solution  of  the  bitumen  under  examination 
is  made  up  to  a  volume  of  100  c.c.  or  reduced  to  that  volume  by 
evaporation.  It  is  then  placed  in  a  500-c.c.  separatory  funnel. 
An  equal  volume  of  the  solvent  naphtha  is  placed  in  another  sepa- 
ratory funnel.  The  naphtha  solution  and  the  naphtha  are  then 
subjected  to  the  action  of  30  c.c.  of  sulphuric  acid  of  specific 


METHODS    OF    ANALYSIS.  545 

gravity  1.84,  the  acid  and  the  naphtha  V>eing  shaken  together  for 
exactly  three  minutes.  This  is  most  important,  since  the  action 
of  the  acid  on  the  hydrocarbons  in  the  bitumen  under  examina- 
tion is  not  a  fixed  one,  but  will  continue  more  or  less  indefinitely. 
After  the  shaking,  the  acid  and  the  naphtha  solution  are  allowed 
to  stand  overnight.  The  acid  is  then  carefully  drawn  off  and  the 
shaking  again  repeated  with  another  volume  of  acid  of  the  same 
amount.  This  will  require  a  shorter  time  for  the  separation  of  the 
acid  and  it  can  be  drawn  off  within  a  few  hours.  If  the  second  acid 
is  very  strongly  discolored  the  acid  treatment  should  be  continued 
a  third  tune.  In  the  case  of  the  blank  determination  with  the 
plain  solvent  one  treatment  will  be  sufficient.  The  naphtha 
solution  and  the  naphtha  are  then  washed  twice  with  water  and 
afterwards  once  with  a  5  per  cent  carbonate  of  soda  solution, 
after  which  one  further  washing  with  water  takes  place.  The 
naphtha  solution  of  the  bitumen  which  is  being  treated  and  the 
blank  naphtha  are  then  poured  into  crystallizing  dishes  3£  inches 
in  diameter  and  2  inches  deep.  In  the  plain  naphtha  is  dissolved 
from  .50  to  .75  gram  of  some  extremely  stable  petroleum  residuum. 
The  two  dishes  are  then  placed  upon  the  steam-bath  to  evaporate 
the  naphtha.  In  order  to  avoid  creeping,  the  sides  of  the  dishes 
are  imbedded  in  a  mass  of  cotton  waste  reaching  to  the  top,  as 
creeping  is  much  diminished  by  having  the  sides  of  the  dish  warm. 
The  evaporation  is  carried  on  on  the  steam-bath  until  the  naphtha 
is  volatilized  and  until  the  blank  shows  on  weighing  that  the 
residue  has  returned  to  its  original  weight.  It  is  then  as- 
sumed that  the  other  dish  is  free  from  naphtha,  and  from 
the  water  which  the  latter  has  dissolved  in  the  process  of  washing. 
This,  under  the  conditions  observed  in  the  author's  laboratory, 
will  require  about  six  hours,  but  the  exposure  on  the  water-bath 
is  generally  continued  one  hour  after  the  blank  has  reached  a 
constant  weight  and  further  for  fifteen  minutes  in  an  air-bath  at 
100°  C.  as  control.  The  results  obtained  in  this  way  are  of  no 
absolute  value,  but  are  of  relative  importance  in  comparing  differ- 
ent fluxes  and  solid  bitumens.  It  cannot,  of  course,  be  applied 
where  the  bitumen  contains  an  appreciable  amount  of  hydro- 
carbons volatile  at  100°  C. 


546  THE  -MODERN   ASPHALT   PAVEMENT. 

Where  62°  naphtha  is  the  solvent  its  volatilization  from  the 
residue  of  bitumen  which  has  been  treated  is  extremely  difficult, 
and  such  a  determination  is,  therefore,  not  recommended. 

Determination  of  Bitumen  Soluble  in  Carbon  Tetrachloride. — 
While  in  the  large  majority  of  cases  the  same,  or  nearly  the  same, 
amount  of  bitumen  is  dissolved  by  carbon  tetrachloride  as  by  bisul- 
phide of  carbon,  bitumens  are  known  in  which  hydrocarbons 
exist  which  are  not  as  soluble  in  the  former  solvent — for  example, 
one  of  the  Venezuelan  asphalts  when  overheated  in  refining, 
grahamite,  and  some  of  the  residual  pitches.  The  use  of  this 
solvent  may,  therefore,  be  desirable  at  times  for  the  purpose  of 
differentiating  the  native  bitumens.  The  insoluble  matter  is 
extremely  fine  and  is  with  difficulty  retained  on  the  closest  filters. 
It  appears  to  coagulate  after  several  hours  and  in  conducting  the 
operation  should  be  allowed  to  stand  over  night  before  filtering. 
A  mild  current  of  air  passed  for  an  hour  through  the  solution 
accomplishes  the  same  purpose,  and  may  be  used  to  hasten 
the  analysis  when  desired. 

One  gram  of  the  sample  is  treated  with  100  cc.  of  the  cold 
solvent,  and  with  the  exception  of  the  precautions  above  noted, 
filtered  in  exactly  the  same  way  as  with  carbon  disulphide. 

The  following  data  are  given  in  illustration  of  the  effect  of 
different  methods  of  handling. 

Filtered  as  soon  as  dissolved 89 .8% 

' '       after  standing  15  hours 83 .6 

"          "          "        48      "     83.6 

"          "     blowing  with  air  1  hour  as  soon  as  dissolved .  .   83 . 5 

The  commercial  supply  of  carbon  tetrachloride  contains  more 
or  less  carbon  disulphide,  and  this  naturally  affects  its  solvent 
power,  so  that  different  lots  may  vary  in  this  respect.  As  the  carbon 
disulphide  is  much  more  volatile  than  the  carbon  tetrachloride, 
the  majority  of  the  latter  can  be  removed  by  redistillation  and 
rejecting  all  that  which  goes  over  below  the  boiling-point  of 
the  carbon  tetrachloride,  76°  C.  It  is  also  possible  that  it  may 
be  removed  by  blowing  a  current  of  air  through  the  carbon  tetra- 
chloride. 


METHODS    OF   ANALYSIS.  547 

Preparation  of  Pure  Bitumen. — The  preparation  of  the  pure 
bitumen  is  a  necessity  where  the  percentage  in  the  crude  or  refined 
material  does  not  exceed  50  per  cent,  as  under  these  circumstances 
its  properties  are  so  much  concealed  by  the  materials  which  are 
mixed  with  it  that  it  is  impossible  to  determine  them,  especially 
the  hardness,  softening  point,  and  other  physical  data.  The 
process  which  has  been  worked  out  for  this  purpose  applies  equally 
well  to  native  bitumens  and  to  artificial  mixtures,  such  as  old 
surfaces  where  it  is  desired  to  determine  the  consistency  of  the 
bitumen  in  the  pavement. 

Such  an  amount  of  crude,  refined  material  or  old  surface  is  taken 
as  analysis  shows  will  afford  about  20  grams  of  pure  bitumen. 
At  the  same  time  20  grams  of  a  bitumen  or  asphalt  cement  of 
corresponding  character  and  of  known  consistency  is  taken  and 
treated  in  the  same  way  as  the  material  under  examination.  JThis 
is  done  for  a  control,  as  will  appear.  The  original  material  and 
that  for  the  control  determination  are  placed,  in  small  pieces, 
in  a  600  c.c.  Erlenmeyer  flask  and  covered  with  300  c.c.  of  redis- 
tilled bisulphide  of  carbon.  This  with  shaking  is  allowed  to  stand 
overnight  or  until  all  lumps  are  broken  down  and  the  bitumen 
is  dissolved.  After  thorough  sedimentation  the  solvent  is  decanted 
as  carefully  as  possible  into  a  litre  flask  and  200  c.c.  of  fresh  bisul- 
phide poured  upon  the  residue.  This  should  be  shaken  and  allowed 
to  stand  again  until  the  insoluble  matter  has  subsided,  when  the 
solution  of  bitumen  is  decanted  as  before  and  added  to  the  first 
300  c.c.  This  process  is  renewed  with  several  portions  of  100  c.c. 
of  bisulphide  until  the  residue  is  clean.  The  entire  solution  is 
allowed  to  stand  overnight,  again  decanted  from  the  finer  sedi- 
ment of  mineral  matter,  and  then  swung  hi  a  centrifugal  machine 
to  remove  as  much  of  the  still  finer  mineral  matter  as  possible. 
If  organic  debris  is  present  the  solution  must  also  be  filtered, 
In  case  a  more  rapid  method  is  desired  for  old  surface  mixtures, 
it  is  probably  quite  as  satisfactory  to  swing  the  solution  obtained 
in  the  first  300  c.c.,  as  this  is,  of  course,  representative  of  the 
total  bitumen,  although  only  a  portion  of  it. 

If  no  centrifugal  is  available  the  different  bisulphide  solutions 
are  well  mixed,  allowed  to  stand  for  some  days  and  decanted. 
The  solutions  of  bitumen,  the  one  holding  that  under  exainina- 


548  THE   MODERN    ASPHALT    PAVEMENT. 

tion  and  the  control,  are,  one  after  the  other,  placed  in  the  same 
flask  and  the  solvent  distilled  off  as  far  as  possible  at  the  heat 
of  a  steam-bath.  The  hot  and  thick  residue  is  poured  into  an 
iron  dish,  the  6-inch-deep-form  sand-bath  already  described. 
This  is  placed  on  a  suitable  sized  hole  on  the  steam-bath  and 
heated.  The  remaining  bisulphide  is  largely  driven  off  in  this 
way.  To  prevent  the  vapor  from  the  hot  bisulphide  from  taking 
fire,  it  will  do  so  without  the  presence  of  flame  in  contact  with 
a  hot  steam-pipe,  or  from  foaming  over,  a  current  of  dry  steam 
is  blown  over  the  surface  of  the  liquid  as  long  as  vapor  is  evolved. 
Finally,  the  presence  of  the  last  traces  of  vapor  are  tested  for 
with  a  small  flame  such  as  is  used  for  determining  the  flashing- 
point  of  oils.  If  all  vapor  of  bisulphide  which  can  be  distilled 
in  this  way  has  disappeared,  the  bitumen  is  in  a  condition  to  be 
brought  over  a  flame  or  sand-bath  and  heated,  with  constant 
stirring,  to  a  temperature  depending  on  its  softness,  and  until  it  is 
sufficiently  fluid  to  be  poured  into  a  tin  box  for  further  treatment. 
This  temperature  should  in  no  case  exceed  325°  F.  These  tin 
boxes  are  of  the  kind  used  in  taking  samples  of  asphalt  cement 
for  penetration  and  shipping  them  to  the  laboratory.  A  con- 
venient form  and  size  is  the  flat,  2-oz.,  screw  top,  Gill  style.1 

The  bitumen  or  bitumens  under  examination  and  the  control 
bitumen,  after  having  been  well  identified  in  the  tin  boxes,  are 
brought  to  the  standard  temperature  and  their  consistency 
determined  with  the  penetrometer.  The  control  will  usually 
be  found  to  be  softer  by  twenty  or  more  points  than  in  the  original 
condition.  If  this  is  the  case  both  or  all  of  the  extracted  bitu- 
mens are  put  in  an  oven  and  heated  for  a  length  of  time  to  300°  F., 
depending  upon  their  excess  of  softness.  It  is  important,  of 
course,  that  the  conditions  in  the  air-bath  are  uniform,  and  that 
the  same  precautions  should  be  used  as  in  the  determination  of 
loss  at  325°  F.  and  400°  F.,  as  previously  described. 

When  the  control  bitumen  has  reached  its  original  known 
consistency  it  is  assumed  that  the  bitumen  or  bitumens  under  exam- 
ination have  done  the  same  thing,  and  the  product  is  taken  as  the 
pure  bitumen  as  it  occurs  in  its  original  consistency  in  the  crude  or 
refined  material  or  of  the  cement  as  it  exists  in  the  surface  mixture. 
1  American  Can  Co.,  New  York. 


METHODS  OF  ANALYSIS. 


549 


Experience  shows  that  this  determination  is  reliable  within 
five  points  on  duplicate  determinations. 

Fixed  Carbon. — The  fixed  carbon  is  determined  usually  on 
the  pure  bitumen  according  to  the  method  recommended  by  the 
Committee  on  Coal  Analysis  of  the  American  Chemical  Society  and 
published  in  the  Journal  of  the  Society  for  1899,  21,  1116.  It  is 
as  follows : 

Place  1  gram  of  pure  bitumen  in  a  "  platinum  crucible  weigh- 
ing 20  or  30  grams  and  having  a  tightly  fitting  cover.  Heat 
over  the  full  flame  of  a  Bunsen  burner  for  seven  minutes.  The 
crucible  should  be  supported  on  a  platinum  triangle  with  the  bottom 
6  to  8  cm.  above  the  top  of  the  burner.  The  flame  should  be 
fully  20  cm.  high  when  burning  free,  and  the  determination 
should  be  made  in  a  place  free  from  draughts.  The  upper  surface 
of  the  cover  should  burn  clear,  but  the  under  surface  should  remain 
covered  with  carbon." 

FIXED  CARBON  IN  BITUMENS. 


Extn 

;mes. 

High 

High. 

Low. 

Grade. 

53.3 

35.3 

53  3 

Albertite.  

54.2 

29.8 

29  8 

Gilsonite  

26.2 

3  3 

14  5 

25  0 

Asphaltenes  from  Trinidad  bitumen  

25  8 

Glance  pitch             .           .  .                 

30  0 

15  0 

15  0* 

Asphalts  .                      

17  9 

10  8 

14  2 

Bverlyte  (artificial  asphalt)  

14  3 

Standard  Asphalt  Co.'s  mine  —  soft  gilsonite.  .  .  . 

7  3 

Malthenes  from  Trinidad  bitumen  

6  3 

Wurtzilite   Utah  ...                

8  8 

5  3 

8  2 

Residuum,  Pennsylvania  field  

3.4 

2  7 

1  Egyptian. 

The  residue  minus  the  small  impurity  of  ash  in  the  pure  bitumen 
is  the  fixed  carbon,  which  should  be  calculated  to  100  per  cent  with 
the  volatile  hydrocarbons,  excluding  the  inorganic  matter.  As 
the  committee  states,  this  determination,  like  most  industrial 
ones,  is  arbitrary,  but  it  is  of  the  greatest  value  in  determining  the 


550  THE  MODERN  ASPHALT  PAVEMENT. 

nature  of  a  bitumen  quickly.  Experience  has  shown  that  true 
hard  asphalts  have  never  been  found  which  yielded  more  than 
17.9  per  cent  or  less  than  10.0  per  cent  of  fixed  carbon,  while 
grahamite  yields  over  53  per  cent,  albertite  over  29  to  54  per  cent, 
and  some  other  bituminous  materials  characteristic  amounts  of 
fixed  carbon. 

EXAMINATION  OF  HEAVY  PETROLEUM  OIL. 

Fluxing  Agents  and  Oils. — The  examination  of  materials 
under  the  above  heading  includes  the  determinations  given  in  the 
accompanying  forms: 

NEW  YORK  TESTING  LABORATORY. 

MAURER;  N.  J., 

Report  on  sample  of  FLUXING  AGENT  received  from. . . . 


Character  of  flux 

Date  when  sample  was  gathered 

Name  of  manufacturer 

Tank-car  number 

Sample  number Test  number 

Specific  gravity,  Beaume —  Actual At  78°  F. 

Flash-point °  F 

Loss,  212°  F., .  '.hours 

Loss,  325°  F.,  7  hours 

Loss,  400°  F.,  7  hours 

Character  of  residue  at  78°  F 

Bitumen  insoluble  in  88°  naphtha,  air  temperature. — Pitch. . 
Per  cent  of  soluble  bitumen  removed  by  H2SO4 

Paraffine  scale 

This  material  is quality 

Remarks: 


METHODS    OF    ANALYSIS.  551 

NEW  YORK  TESTING  LABORATORY. 

MAURER,  N.  J., 

Test  number: 

Source  of  supply 


PHYSICAL  PROPERTIES. 
Specific  gravity,  dried  at  212°  F.,  78°  F./780  F. .. . 


Flows,  cold  test 

Color 

Odor 

Under  microscope 

Flashes,0  F.,  N.  Y.  State  oil-tester 
Viscosity 


CHEMICAL  CHARACTERISTICS. 
Original  substance: 

Loss,  212°  F.,  1  hour  or  until  dry 

Dry  substance : 

Loss,  325°  F.,  7  hours 

Character  of  residue 

Penetration  of  residue  at  78°  F 

Loss,  400°  F.,  7  hours  (fresh  sample) 

Character  of  residue 

Penetration  of  residue  at  78°  F 


Bitumen  soluble  in  CS2,  air  temperature. 

Difference 

Inorganic  or  mineral  matter 


Bitumen  insoluble  hi  88°  naphtha,  air  temperature. — Pitch. . 

Per  cent  of  soluble  bitumen  removed  by  H.jSO4 

Per  cent  of  bitumen  as  saturated  hydrocarbons 


Per  cent  of  solid  paraffines. 


Bitumen  yields  on  ignition:  «, 

Fixed  carbon . .... 

Ultimate  composition: 


Remarks: 


552  THE   MODERN    ASPHALT    PAVEMENT. 

The  methods  used  in  making  these  determinations  are,  as  a 
whole,  the  same  as  those  described  for  hard  asphalts  with  the 
following  modifications. 

Specific  Gravity. — The  specific  gravity  of  oils  or  fluxes  is 
taken  on  the  material  either  dried  at  212°  F.,  or,  if  there  are  light 
oils  present,  volatile  at  this  temperature,  on  some  of  the  oil  freed 
from  water  by  being  swung  in  the  centrifugal. 

Heavy  fluxes  too  dense  to  employ  a  picnometer  with  are  filled 
into  an  open  specimen  tube,  10  cm.  long,  2  cm.  in  diameter, 
and  holding  about  27  grams  of  water,  even  with  the  top,  which 
is  ground  flat  and  parallel  to  the  base.  The  weight  of  this  volume 
of  oil  at  78°  F.  is  compared  with  that  of  water  at  the  same  tempera- 
ture. Lighter  oils  are  examined  with  the  picnometer  or  Westphal 
balance.  The  industrial  methods  for  the  determination  of  the 
specific  gravity  of  dense  oils  admit  of  much  improvement  and  are 
now  probably  not  accurate  beyond  the  second  place  of  decimals. 

Mr.  Lester  Kirschbraun,  chemist  of  the  Chicago  City  Labor- 
atory, Bureau  of  Engineering,  describes  the  following  method 
which  is  employed  by  him  satisfactorily. 

Take  a  test  tube  about  a  half  inch  in  diameter  and  cut 
it  off  to  give  a  1J  inch  by  i  inch  tube.  Flare  it  out  to  carry  a 
fine  wire.  Put  about  10  grams  of  the  oil  or  asphalt  into  it, 
and  suspend  it  in  an  oven  to  remove  air  bubbles  and  drive  off  the 
water.  Cool  and  weigh  accurately  in  air  and  immerse  in  distilled 
water  at  25°  C.  to  a  fixed  mark  on  the  wire  and  weigh.  Previous 
to  filling  the  tube  with  the  sample,  determine  its  weight  carefully 
in  air  and  in  water  at  25°  C.,  immersed  to  the  fixed  mark.  These 
weighings  give  the  weights  of  the  tube  alone,  in  air  and 
in  water,  and  the  combined  weights  of  the  tube  and  the  sample, 
in  air  and  water.  The  gravity  is  calculated  in  this  way,  represent- 
ing. 

Weight  of  tube  in  air a 

Weight  of  tube  and  sample  in  air 6 

Weight  of  tube  in  water c 

Weight  of  tube  and  sample  in  water d 

Wt.  in  air  of  sample 

bD.    gT.  =  9 f, ; 

Loss  of  wt.  in  water 


METHODS    OF    ANALYSIS.  553 

in  this  case  becomes 

7H      !T\ TA      IT*    •••••••      V-*'/ 


When  the  gravity  of  the  sample  is  less  than  unity,  the  second 
expression  in  the  denominator  is  a  negative  (d—  c)quantity  and 
is  added  to  the  original  weight  of  the  sample  (b  —  a),  inasmuch  as 
the  buoyancy  of  the  sample  will  overcome  its  own  weight  and 
to  a  certain  extent  will  also  reduce  the  weight  of  the  tube  in  water, 
making  c  greater  than  d. 

The  formula  in  this  case  may  be  also  expressed  so: 


(2) 


When  the  gravity  of  the  sample  is  greater  than  unity,  d 
will  be  greater  than  c  and  the  first  formula  applies  without 
confusion.  As  an  example,  take  a  blown  oil,  the  gravity  of  which 
was  determined  in  our  laboratory  according  to  this  method. 

Weight  of  tube  in  air " a  =  4 .7870 

Weight  of  tube  and  sample  in  air 6  =  16 .7900 

Weight  of  tube  in  water,  25°  C c  =  2 .8565 

Weight  of  tube  and  sample  in  water d  =  2 .6425 

by  formula  (2) 

16.7900-4.7870 =12.003p  = 

~  (16.7900-4.7870)  +(2.8565-2.6425)  "  12.2170" 

This  may  seem  a  bit  complicated  at  first,  but  it  will  be  noted 
that  the  factors  a  and  c  are  constants  which  can  be  used 
for  the  same  tube  without  change,  and  the  calculation  becomes 
very  simple  after  a  few  trials. 

The  advantages  of  the  method  are  in  doing  away  with  the 
inconveniences  of  handling  a  large  amount  of  oil,  and  the  ease 
with  which  air  bubbles  can  be  removed,  particularly  in  handling 
refined  asphalt.  Of  course  it  can  be  used  only  with  oils  which 
are  viscous  enough  to  be  retained  in  the  tube  when  under  water. 


554  THE    MODERN    ASPHALT   PAVEMENT. 

Flow  Test. — Some  of  the  oil  is  chilled  in  a  large  test-tube  and 
gradually  allowed  to  attain  the  temperature  of  the  room.  The 
point  at  which  it  will  flow  in  the  inclined  tube  is  the  flow-point. 

Color. — This  is  found  by  examining  the  reflection  from  the 
surface  of  the  cold  oil.  It  is  intended  to  be  that  revealed  by 
reflected  and  not  by  transmitted  light  through  a  thin  film. 

Odor. — The  odor  can  be  described  as  that  corresponding  to 
different  kinds  of  known  petroleum  in  the  cold  or  on  heating. 

Microscopic  Examination. — The  appearance  of  an  oil  that  has 
been  heated  is  noted  under  the  microscope  to  determine  the  presence 
of  material  insoluble  in  the  main  mass  of  the  oil. 

Flash-point. — The  flash-point  is  determined  in  a  New  York 
State  oil-tester.1  The  water-bath  is  of  course  removed  and  the 
oil  heated  directly  with  a  flame  of  a  size  to  raise  the  temperature  at 
the  rate  of  20°  per  minute  and  a  small  flame  from  a  capillary  glass 
or  metal  tube  is  used  for  flashing.  The  flame  should  be  applied 
at  5°  intervals.  The  determination  should  be  repeated  on  such  oils 
as  flash  at  unexpected  temperatures.  The  water  must  be  removed 
from  the  oil  or  flux  before  putting  it  in  the  tester  cup,  either  by  heat 
or  by  the  centrifugal. 

Open  tests  of  high  flashing  oils  are  not  reliable  and  at  the 
best  with  the  closed  tester  a  reading  of  5°  intervals  only  need  be 
sought. 

Viscosity. — Thf>  Engler  viscosimeter  is  used  for  this  purpose, 
it  being  available  for  temperatures  as  high  as  500°  C. 

The  rate  of  flow  in  seconds  of  time  is  compared  with  that  of 
an  equal  volume^  of  water  at  the  same  or  some  standard  tem- 
perature. 

Loss  at  212°  F.— The  water  or  loss  of  light  oils  at  212°  F.  is 
determined  by  weighing  out  20  grams  in  a  glass  or  tin  dish,  such 
as  is  described  for  use  in  the  determination  of  loss  at  325°  F.  in 
hard  asphalts,  and  heating  in  the  oven  described,  at  the  temper- 
ature named,  until  the  oil  has  ceased  foaming,  or  to  practically 
constant  weight.  The  precautions  previously  noted  should  be 
observed.  When  oils  contain  a  large  percentage  of  water  this  is 

1  E.  &  A.,  No.  4160. 


METHODS    OF    ANALYSIS.  555 

better  determined  by  the  centrifugal  method  or  by  dilution  with 
naphtha. 

Drying  an  oil  or  flux  for  subsequent  examination  is  done  by 
heating  a  large  volume  in  an  iron  dish  over  a  flame,  with  constant 
stirring,  unless  it  contains  much  light  oil,  when  the  centrifugal 
method  alone  can  be  used. 

Loss  at  325°  F.  and  400°  F.  in  Seven  Hours. — Separate  portions 
of  20  grams  of  the  dried  material  are  taken  for  each  determina- 
tion and  are  heated  to  these  temperatures  in  the  manner  described 
for  solid  bitumens.  The  residues  from  the  oils  and  fluxes  are 
examined  after  heating  to  these  temperatures  more  in  detail  than 
those  from  hard  asphalts  which  have  been  treated  similarly. 

After  cooling  and  weighing  the  appearance  of  the  residue  is 
noted,  especially  as  to  whether  it  is  smooth  or  granular  owing  to  the 
presence  of  paraffine,  the  temperature  at  which  it  flows,  whether 
it  pulls  out  to  a  long  string  or  is  short.  If  it  is  so  hard  that  it  does 
not  flow  except  on  raising  the  temperature  above  100°  F.,  its  con- 
sistency is  determined  with  the  penetrometer  either  at  100°  F.  or 
at  78°  F.  or  at  lower  temperatures. 

The  residue  should  also  be  examined  under  the  microscope  to 
determine  whether,  owing  to  the  nature  of  the  fluxes,  they  have 
been  at  all  decomposed  at  these  temperatures  with  a  separation 
of  insoluble  pitch,  which  is  an  evidence  that  the  original  flux  must 
have  been  more  or  less  cracked  in  the  process  of  manufacture. 

Total  Bitumen ;  Inorganic  Matter  and  Naphtha  Soluble  Bitu- 
men.— These  determinations  are  arrived  at  by  the  methods 
already  described  for  hard  asphalts. 

As  the  oils  and  fluxes  are  more  easily  soluble  it  is  unnecessary 
to  let  the  solvents  act  on  them  for  so  long  a  time  as  in  the  case 
of  hard  asphalts.  There  is  little  object  in  using  62°  naphtha  with 
oils  or  fluxes,  as  there  is  too  little  difference  between  its  solvent 
power  and  that  of  bisulphide  of  carbon  with  such  materials  to  make 
it  worth  while.  The  residue  insoluble  in  88°  naphtha,  however, 
shows  how  much  decomposition  there  has  been  in  fluxes  which 
have  been  subjected  to  excessive  heat. 

Determination  of  the  Character  of  the  Hydrocarbons  in  Fluxes. 
— The  character  of  the  hydrocarbons  in  any  of  the  heavy  oils  used 


556  THE   MODERN    ASPHALT    PAVEMENT. 

for  fluxing  purposes  is  determined  by  treatment  with  sulphuric 
acid  after  the  method  described  for  use  with  malthenes  from  hard 
asphalts. 

Determination  of  the  Amount  of  Hard  Paraffine  Scale. — The 
amount  of  hard  paraffine  scale  contained  in  any  flux  or  heavy 
oil  can  be  readily  determined  by  the  author's  modification1  of 
the  method  of  Holde.2 

The  method  in  detail  is  as  follows: 

The  Determination  of  Paraffine  in  Petroleum  Residues, 
Asphaltic  Oils,  and  Asphalts  Fluxed  with  Paraffine  Oils.— For 
this  purpose,  one,  two,  or  more  grams,  of  the  substance  to  be  ex- 
amined is  taken  and  covered  in  an  Erlenmeyer  flask  with  100  c.c. 
of  88°  naphtha.  The  amount  will  depend  on  the  paraffine  present 
and  on  the  percentage  of  oil  which  remains  after  the  preliminary 
treatment  with  naphtha  and  acid.  Of  a  residuum  from  east- 
ern pipe-line  oils  one  gram  is  sufficient,  as  the  substance  con- 
sists of  a  nearly  pure  bitumen  containing  from  4  to  12  per  cent  of 
paraffine.  Ten  grams  of  a  residual  pitch  from  asphaltic  oil  should 
be  used,  as  this,  in  some  cases,  contains  only  65.0  per  cent  of  its 
bitumen  soluble  in  naphtha,  less  than  50  per  cent  unacted  on  by  acids, 
and  only  about  1.0  per  cent  paraffine.  Several  grams  can  be  taken 
of  a  Trinidad  asphalt  cement,  made  of  asphaltum  and  paraf- 
fine residuum,  which  contains  26.0  per  cent  of  mineral  matter 
and  only  70.0  per  cent  of  its  bitumen  is  in  a  form  soluble  in  88° 
naphtha. 

The  object  of  the  naphtha  treatment  is  to  separate  the  paraffine 
from  substances  of  a  non-bituminous  nature  and  from  some  of 
the  asphaltic  hydrocarbons  insoluble  in  naphtha  which  would 
be  precipitated  in  the  ether  alcohol  solvent  and  contaminate  the 
paraffine. 

By  this  means  all  the  unsaturated  hydrocarbons  and  those 
of  an  asphaltic  nature,  readily  precipitated  by  alcohol  from 


1  J.  Soc.  Chem.  Ind.,  1902,  21,  690. 

2  Mitt.  a.  d.  Konig,  tech.  Vers-anst,  Berlin,  1896,  14,  211.     Abs.  J.  Soc. 
Chem.  Ind.,  1897,  16,  362.     Lunge,  Chem.  tech.,  Untersuchungs,  Methoden. 
3.9. 


METHODS    OF    ANALYSIS. 


557 


their  ether    solution,   are    removed   and   the  possibility  brought 
about  of  recovering  the  paraffine  in  a  pure  condition. 

Some  determinations  made  in  the  manner  described  resulted 
as  follows: 


PETROLEUM  RESIDUUM  FROM  PIPE-LINE  OIL. 
Specific  gravity,  0.93. 


Number. 

Weight 
taken. 

Soluble  in  Naphtha. 

Not  acted  on  by 
H£(V 

Paraffine. 

1 

Grams. 

1.0 

Per  Cent. 
96.0 

Per  Cent. 
No  treatment 

Per  Cent. 

7.95 

2 

1.0 

96.0 

89.5 

5.55 

3 

1.0 

Distilled  in  vacua 

No  treatment 

5.95 

TRINIDAD  ASPHALT  CEMENT. 


Number. 

Weight  Taken, 
Grams. 

Soluble  in  Naphtha. 

Not  Acted  on  by 

H2SC-4. 

Paraffine. 

1 

10  0 

No  treatment 

2  95 

2 

10  0 

Treated 

0  95 

In  each  case  the  paraffine  recovered  after  treatment  was  white 
and  pure,  while  that  obtained  in  the  other  way,  even  by  distilla- 
tion in  vacuo,  was  colored.  The  results  after  treatment  were,  of 
course,  lower  and  more  correct. 

The  Trinidad  asphalt  cement  was  made  from  100  parts  of 
Trinidad  asphalt  and  20  parts  of  a  residuum  similar  to  the  one 
analyzed.  The  asphalt  contained,  of  course,  no  paraffine;  the 
residuum,  5.55  per  cent.  The  calculated  amount  in  the  cement 
is  therefore  0.925  per  cent,  and  0.95  per  cent  was  found. 

In  this  way  it  can  be  determined  whether  the  flux  which  has 
been  used  in  the  preparation  of  an  asphalt  cement  has  been  derived 
from  paraffine  petroleum  or  from  one  having  an  asphaltic  base, 
since  if  paraffine  is  found  to  such  an  extent  as  shown  above  it  will 
necessarily  point  to  the  use  of  a  paraffine  flux,  as  no  native  solid 
bitumen  hi  use  in  the  paving  industry  contains  paraffine. 


558  THE    MODERN    ASPHALT    PAVEMENT. 

Rapid  Method  for  Paraffine  in  Crude  Petroleum  Fluxes  and 
Residues.1  Standard  Oil  Company. — The  preceding  method,  while 
not  lacking  in  accuracy,  cannot  be  completed  in  a  single  day,  and 
the  following  method,  while  yielding  lower  results,  has  the  ad- 
vantage of  rapidity. 

One  hundred  grams  of  the  oil  is  distilled  rapidly  in  a  6-oz. 
retort  to  dry  coke. 

Five  grams  of  the  well  mixed  distillate  is  treated  in  a  2-oz.  flask 
with  25  cc.  Squibb's  ether;  after  mixing  together  thoroughly, 
25  cc.  Squibb's  absolute  alcohol  is  added,  and  the  flask  packed 
closely  in  a  freezing  mixture  of  finely  crushed  ice  and:  salt  for  at 
least  thirty  minutes.  Filter  off  the  precipitate  quickly  by  means  of 
a  suction  pump,  using  a  No.  575  C.  S.  &  S.  9-cm.  hardened  filter, 
cooled  by  the  above  freezing  mixture  in  a  suitable  apparatus. 

Rinse  and  wash  the  precipitate  with  1  to  1  Squibb's  alcohol 
and  ether  mixture  cooled  to  0°  F.  until  free  from  oil.  Fifty  cc. 
of  the  washed  solution  is  usually  sufficient.  When  sucked  dry, 
remove  the  paper,  transfer  the  waxy  precipitate  to  a  small  glass 
crystallizing  dish.  Dry  on  a  steam  bath  and  determine  the 
weight  of  paraffine  scale  remaining  in  the  dish. 

Calculation. — Weight  of  paraffine  scale  divided  by  weight  of 
distillate  taken  and  multiplied  by  per  cent  of  total  distillate  ob- 
tained from  original  sample,  equals  per  cent  of  paraffine  scale. 

Fixed  Carbon. — This  determination  is  sometimes  desirable 
with  fluxes,  especially  with  harder  ones,  to  show  the  same  facts 
revealed  by  the  88°  naphtha  extract.  It  is  carried  out  in  the 
same  way  as  with  hard  bitumen. 

Asphalt  Cement. — Asphalt  cement  is  examined  to  determine 
its  consistency,  the  amount  of  bitumen,  inorganic  or  mineral 
matter  and  organic  matter,  not  soluble,  it  contains.  Rarely  the 
naphtha  soluble  bitumen  is  extracted  and  examined  to  determine 
the  nature  and  quantity  of  the  flux  of  which  it  has  been  made. 
The  permanency  of  its  consistency,  when  it  is  maintained  in  a 
melted  condition  at  325°  F.  for  some  time,  may  be  noted. 

The  consistency  of  asphalt  cement  is  determined  in  several 
ways,  the  most  desirable  of  which  in  the  laboratory  is  the  pene- 

1  Kindly  furnished  by  Mr.  George  M.  Saybolt. 


METHODS   OF  ANALYSIS.  559 

tration  machine,  for  the  reason  that  it  admits  of  an  absolute  record 
in  figures.  Penetration  machines  have  been  designed  by  Bowen, 
Kenyon,  Dow,  and  tho  New  York  Testing  Laboratory.  The  two 
latter,  however,  have  superseded  the  earlier  and  less  desirable  types. 

The  flow  test  originated  by  the  Warren-Scharf  Asphalt  Paving 
Company,  as  well  as  the  test  by  chewing,  which  is  a  rough  one 
but  always  available,  are  of  decided  value  and  convenience  for 
use  at  plants. 

The  construction  of  the  various  penetration  machines  and  the 
method  of  using  them  is  described  as  follows: 

Bowen's  Penetration  Machine  or  Viscosimeter  for  Bitumi- 
nous Solids. — Principle  of  the  Machine. — The  machine,  Fig.  34,  is 
designed  to  register  on  a  dial  in  degrees,  arbitrarily  selected,  the 
depth  to  which,  a  No.  2  cambric  needle,  attached  to  a  weighted 
arm  or  lever,  penetrates  into  the  surface  of  the  material  to  be 
tested  when  allowed  to  act  upon  it  for  one  second  at  a  standard 
temperature. 

The  machine  has  been  described  by  H.  C.  Bowen,  in  the 
School  of  Mines  Quarterly,  10,  297. 

The  Dow  Penetration  Machine. — A  penetration  machine  has 
been  designed  by  Mr.  A.  \V.  Dow,  formerly  Inspector  of  Asphalt  and 
Cements,  of  the  District  of  Columbia,  Washington,  D.  C  ,  which  in  so 
far  as  it  is  based  on  the  measurement  of  the  millimeters  to  which  a 
definite  needle  penetrates  into  the  asphalt  cement  under  a  definite 
weight  at  a  definite  temperature  is  concerned,  is  a  more  truly 
scientific  instrument  than  the  one  previously  described.  The  read- 
ings by  this  machine  are  about  20  points  lower  than  those  obtained 
with  the  Bowen  instrument,  but  it  possesses  the  disadvantage 
that  when  large  numbers  of  asphalt  cements  are  to  be  examined 
at  any  one  time  it  requires  greater  delicacy  of  manipulation  and 
much  more  time  than  is  the  case  when  the  Bowen  machine  is 
used.  Fig.  35.  Mr.  Dow  describes  its  use  as  follows: 

"  Description  and  Directions  for  Using  the  Dow  Penetration 
Machine. — The  object  of  the  penetration  test  is  to  ascertain  the 
softness  of  asphalt,  etc.,  and  is  accomplished  by  determining  the 
distance  a  weighted  needle  will  penetrate  into  the  specimens  under 
examination. 


560  THE    MODERN   ASPHALT   PAVEMENT. 


FIG.  34.— Bowen  Penetration  Machine. 


METHODS  OF  ANALYSIS. 


561 


"So  that  all  tests  may  be  comparable,  a  standard  needle 
should  be  used,  weighted  with  a  constant  weight.  The  tests  should 
be  made  on  samples  at  a  standard  temperature  and  be  made  for 


•0- 


A        H 


W 


FIG.  35. — Dow  Penetration  Machine. 

the  same  length  of  time  in  every  case.  The  standards  used  in 
this  machine  for  testing  cements  to  see  that  they  are  of  uniform 
consistency  are  a  No.  2  needle,  weighted  with  100  grams,  pene- 
trating for  five  seconds  into  the  sample  at  a  temperature  of  of  77°  F. 
(25°  C.) 

"  The  apparatus   consists  of  a  No.  2  needle  A,  inserted  in  a 


562  THE  MODERN  ASPHALT  PAVEMENT. 

short  brass  rod  which  is  held  in  the  aluminum  rod  C  by  the 
binding  screw  B.  The  aluminum  rod  is  secured  in  a  frame- 
work so  weighted  and  balanced  that  when  it  is  supported  on  the 
point  of  the  needle  A  the  framework  and  rod  will  stand  in  an 
upright  position,  allowing  the  needle  to  penetrate  perpendicu- 
larly without  the  aid  of  a  support,  thus  doing  away  with  any 
friction. 

"  The  frame,  aluminium  rod,  and  needle  weigh  100  grams  with 
the  weight  on  bottom  of  frame ;  without  weight  50  grams.  Thus 
when  the  point  of  the  needle  rests  on  the  surface  of  the  sample 
of  material  to  be  tested  as  to  the  penetration,  it  will  penetrate 
into  the  sample  under  a  weight  of  100  grams  or  50  grams  as  desired. 

"  The  needle  and  weighted  frame  are  shown  in  Fig.  35,  side 
and  front  views  of  the  entire  apparatus  put  together  and  ready 
for  making  a  penetration.  D  is  the  shelf  for  the  sample,  E, 
is  the  clamp  to  hold  the  aluminum  rod  C  until  it  is  desired 
to  make  a  test,  F  is  a  button  which  when  pressed  opens  clamp  E. 
By  turning  this  button  while  the  clamp  is  being  held  open  it  will 
lock  and  keep  the  clamp  from  closing  until  unlocked.  The  device 
to  measure  the  distance  penetrated  by  the  needle  consists  of  a 
rack,  the  foot  of  which  is  G.  The  movement  of  this  rack  up  or 
down  turns  a  pinion  to  which  is  attached  the  hand  which  indicates 
on  dial  K  the  distance  moved  by  the  rack.  One  division  of  the 
dial  corresponds  to  a  movement  of  the  rack  of  1/100  cm.  The  rack 
can  be  raised  or  lowered  by  moving  counterweight  H  up  or  down. 
L  is  a  tin  box  containing  sample  to  be  tested  which  is  covered 
with  water  in  the  glass  cup,  thus  keeping  its  temperature  constant. 
MM'  are  leveling  screws.  A  clock  movement  having  a  10-inch 
pendulum  is  attached  to  the  wall  to  one  side  of  the  machine.  Make 
a  mark  P  on  the  wall  just  at  the  extremity  of  the  swing  of  the 
pendulum;  a  double  swing  of  this  pendulum,  that  is  from  the  time 
it  leaves  P  until  it  returns,  is  one  second. 

"  The  only  other  things  necessary  to  complete  the  outfit  are  a 
large  dish-pan,  a  pitcher  to  hold  ice-water  and  a  tin  for  hot  water; 
a  coffee-pot  is  a  good  thing. 

"  To  make  penetration  tests  place  the  materials  contained  in 
circular  tins,  along  with  the  glass  dish,  under  five  or  six  inches  of 


METHODS  OF  ANALYSIS.  563 

water  in  the  dish-pan,  which  should  have  been  previously  brought 
to  a  temperature  of  77°  F.  by  the  addition  of  hot  water  or  cold 
water. 

"  While  the  sample0  are  under  the  water  it  should  be  stirred 
every  few  minutes,  with  the  thermometer  and  the  temperature 
kept  constant  at  77°  F.  by  the  addition  of  hot  or  cold  water  as  the 
case  may  require.  The  samples  should  remain  under  the  water  for 
at  least  fifteen  minutes  and  in  cases  where  they  are  very  cold  or 
hot,  at  least  one-half  hour.  The  most  expeditious  way  to  proceed  in 
testing  a  sample  just  taken  from  a  still  or  tank  is  to  immerse  it  in 
ice-water  as  soon  as  it  has  hardened  sufficiently  and  keep  it  there  for 
ten  minutes,  then  in  the  water  at  77°  F.  and  keep  it  there  for  fifteen 
minutes.  When  the  sample  has  remained  in  the  water  for  the  speci- 
fied time  it  is  ready  to  penetrate. 

"  The  aluminum  rod  C  should  be  pressed  up  through  the  clamp 
E  so  that  it  will  be  at  such  a  height  that  the  glass  cup  will  easily 
pass  under  it  when  placed  on  shelf  D. 

"  A  sample  in  tin  box  should  now  be  placed  in  the  glass  cup  and 
removed  in  it  covered  with  as  much  water  as  convenient  without 
spilling. 

"  The  glass  cup  containing  sample  is  placed  on  shelf  D  under 
C.  Insert  brass  rod  with  needle  into  C  and  secure  by  tightening 
binding  screw  B,  lower  C  until  the  point  of  the  needle  very  nearly 
touches  surface  of  sample;  then,  by  grasping  the  frame  with  two 
hands  at  S  and  S',  cautiously  pull  down  until  needle  is  just  in  con- 
tact with  surface  of  sample. 

"  This  can  best  be  seen  by  having  a  light  so  situated  that, 
looking  through  the  sides  of  the  glass  cup,  the  needle  will  be  reflected 
in  the  surface  of  the  sample.  After  thus  setting  the  needle,  raise 
counterweight  H  slowly  until  the  foot  of  the  rack  G  rests  on 
the  head  of  rod  C;  note  reading  of  dial,  place  thumb  of  right 
hand  on  R  and  press  button  F  with  forefinger,  thus  opening  the 
clamp. 

"  Hold  open  for  five  seconds  and  then  allow  it  to  close.  The 
difference  between  the  former  reading  of  the  dial  and  the  present 
is  the  distance  penetrated  by  the  needle,  or  the  penetration  of  the 
sample.  Raise  rack,  loosen  binding  screw  B  raise  rod  through 


564  THE  MODERN  ASPHALT  PAVEMENT. 

clamp,  leaving  the  needle  sticking  in  sample.  Remove  needle 
from  sample,  clean  well  by  passing  through  a  dry  cloth,  replace 
needle  in  C  and  the  machine  is  ready  for  another  test. 

"  Do  not  clean  needle  on  oily  cloth,  or  waste. 

"  Do  not  allow  rack  to  descend  too  rapidly  on  rod  C  as  it 
may  force  C  through  the  clamp,  thus  spoiling  the  reading. 

"  After  using  the  machine,  leave  it  so  the  top  of  the  rack  is 
just  level  with  its  base.  You  will  thus  prevent  dust  from  entering 
and  getting  into  pinion.  When  not  in  use  keep  machine  covered 
with  a  cloth  to  protect  from  dust. 

"  Examine  point  of  needle  from  time  to  time  with  magnifying 
glass  to  see  that  it  is  not  injured  in  any  way. 

"If  the  needle  is  found  defective  remove  by  heating  the  brass 
rod,  when  the  needle  can  be  withdrawn  with  pincers.  Break  eye 
from  one  of  the  extra  needles  and  press  into  brass  rod  previously 
heated. 

"  If  needle  does  not  stay  in  well,  insert  it  with  a  small  lump  of 
asphalt. 

"If  when  this  framework  is  supported  on  the  point  of  the 
needle  it  does  not  balance  so  that  the  aluminum  rod  C  stands 
perfectly  perpendicular,  the  frame  is  bent  and  should  be  straight- 
ened until  the  rod  stands  perpendicular.  This  can  easily  be  done 
by  hand. 

"If  rack  G  does  not  descend  readily  of  its  own  weight  when 
counter  weight  H  is  raised,  it  is  likely  that  dust  has  gotten  into 
the  pinion.  To  get  at  pinion  to  clean,  remove  dial  K  and  bear- 
ing T,  when  pinion  can  be  pulled  out  sufficiently  far  to  clean. 

"Never  oil  rack  and  pinion,  as  it  prevents  a  free  movement 
of  rack. 

"If  machine  is  unsatisfactory  write  and  explain  trouble. 

"Test  for  Susceptibility  to  Changes  in  Temperature. — The 
standards  that  I  have  adopted  for  this  test  are: 

"The  distance  penetrated  by  the  No.  2  needle  into  the  sample 
at  32°  F.  in  one  minute  with  200  grams  on  frame. 

"The  penetration  at  77°  F.,  as  described  before,  and  the  pene- 
tration into  the  sample  of  the  No.  2  needle  in  five  seconds  at  100°  F. 
with  50-gram  frame.  In  some  cases  I  use  100  grams,  which 


METHODS  OF  ANALYSIS. 


565 


is  preferable  if  the  depth  of  the  sample  will  permit.  In  all  cases 
when  you  give  a  penetration  of  cement  state  in  parentheses  how 
it  was  made,  as  for  example  (No.  2N.,  5  sec.,  50  grams,  100°) 
means  that  the  penetration  was  made  with  a  No.  2  needle  pene- 
trating 5  seconds  with  50-gram  frame  at  100°  F. 

"If  a  statement  is  made  like  this  there  can  never  be  any  doubt 
about  the  figures  and  they  will  be  understood  by  all  familiar  with 
the  machine." 

New  York  Testing  Laboratory  Penetrometer, — In  the  Dow  in- 


FIG.  30. 


strument,  all  the  parts  are  of  very  light  construction  and  require 
a  certain  delicacy  of  touch  to  use  it  satisfactorily,  and  consequent- 


566 


THE    MODERN  ASPHALT    PAVEMENT. 


ly;  it  is  not  easily  manipulated  by  such  men  as  are  found  at  paving 
plants,  although  these  disadvantages  are  of  slight  consideration 
in  the  laboratory.  The  shelf  upon  which  the  sample  to  be  tested 
is  placed  is  fixed  and  the  needle  must,  therefore,  be  brought 


FIG.  37. 

down  toward  the  surface  of  the  bituminous  cement  until  it  is  in 
contact  Avith  it.  On  each  side  of  the  shelf  which  holds  the  sample 
are  the  twro  rods,  of  the  frame  from  which  the  weight  which  acts 
upon  the  needle  is  suspended.  These  are  much  in  the  way  in 
adjusting  the  needle  in  contact  with  the  surface  of  the  bituminous 
cement,  and  restrict  the  size  of  the  sample  of  the  latter. 


METHODS    OF   ANALYSIS.  567 

In  the  Penetrometer  (Figs.  36  arid  37),  an  attempt  has  been 
made  to  overcome  these  features,  without  seriously  imparing  the 
accuracy  of  the  instrument.  The  sample  to  be  tested,  which  may, 
if  desired,  be  of  large  or  small  size,  is  placed  upon  a  table  which  is 
supported  upon  a  screw,  enabling  the  needle  to  be  set  at  zero, 
and  the  sample  to  be  brought  up  to  contact  with  the  point  by 
elevating  it  with  the  screw.  The  entire  weight  acting  upon  the 
needle  is  contained  in  the  tube  which  holds  it,  and.  being  placed 
at  the  lowest  possible  point  in  the  tube,  does  not  tend  to  seriously 
divert  it  from  the  vertical  on  the  release  of  the  clamp  and  makes 
it  possible  to  do  away  with  the  frame  which  is  so  much  in  the 
way  in  the  Dow  apparatus.  The  Penetrometer  is  given  greater 
stability  than  the  Dow  apparatus  by  making  a  much  larger  and 
firmer  clamp  to  hold  the  tube,  while  all  the  other  parts  of  the 
instrument  are  rigidly  constructed.  The  increased  friction  of 
the  clamp  on  the  rod  reduces  the  extent  of  the  penetration  of 
the  needle  by  one-  or  two-tenths  of  a  millimeter,  but  this  is  prac- 
tically of  no  consequence,  as  it  is  a  variation  not  greater  than  that 
due  to  different  needles  or  to  the  personal  equation  of  various 
operators. 

The  determination  of  the  depth  to  which  the  needle  has  pen- 
etrated is  arrived  at  by  a  similar  means  to  that  employed  in  the 
Dow  machine,  a  rack  and  pinion,  but  the  rod  to  which  the  rack 
is  attached  is  prevented  from  moving,  not  by  a  balance  weight 
attached  to  a  cord,  as  in  the  Dow  machine,  but  by  a  spring  ex- 
erting a  slight  pressure  against  its  side.  This  does  away  with  the 
opportunity  for  the  cord  and  balance  weight  to  be  knocked  out 
of  place  or  lost,  and  makes  the  apparatus  much  more  convenient 
to  move  from  place  to  place.  The  penetration  of  the  needle  is 
registered  in  tenths  of  millimeters,  on  the  same  scale  as  in  the 
Dow  machine,  and  the  time  during  which  the  weight  acts  is  made 
five  seconds  instead  of  one,  as  is  the  case  of  the  Bowen  apparatus. 
The  detail  of  the  manipulation  of  the  tests  is  the  same  with  the 
Penetrometer  as  with  the  Dow  apparatus,  previously  described. 

The  Penetrometer  is  manufactured  by  Messrs.  Howard  & 
Morse,  1197  DeKalb  Avenue,  Brooklyn,  X.  Y. 

Flow  Test. — The  consistency  of  asphalt  cements  can  also  be 
controlled  by  means  of  a  flow  test.  This  is  a  comparative  one 


568 


THE    MODERN    ASPHALT    PAVEMENT. 


and  gives  nothing  but  ocular  evidence  as  to  the  relative  softness 
of  two  cements  at  or  near  their  flowing  point.  The  test  consists 
in  making,  in  a  suitable  mould,  cylinders  f  inch  long  and  f  inch 
in  diameter,  of  a  standard  cement  and  of  the  one  to  be  examined, 
placing  them  on  a  brass  plate  with  corrugations  corresponding 
in  size  to  that  of  the  cylinders  and  exposing  them  at  an  angle  of 
45°  to  a  temperature  at  which  the  cements  will  soften  and  flow. 


FIG.  38.—  Flow  Plate. 

Cements  made  of  the  same  asphalt  and  flux  are  of  the  same  con- 
sistency if  they  flow  to  the  same  length,  Fig.  38. 

As  a  quick,  rough  test  this  is  very  satisfactory;  but  care  must 
be  taken  that  the  cylinders  are  exposed  to  a  uniform  temperature 
and  that  one  part  of  the  brass  plate  is  not  hotter  than  another, 
which  may  readily  happen  if  it  touches  hot  metal  or  any  good 


METHODS  OF  ANALYSIS.  569 

conductor.  The  plate,  for  safety,  should  only  be  warmed  by  air 
and  should  be  isolated  from  contact  with  metals  by  asbestos,  paper 
or  wood. 

Cylinders  are  made  by  softening  the  cement  to  be  examined 
until  it  can  be  rolled  out  on  a  board  to  about  the  proper  size.  It 
is  then  pressed  in  a  brass  mould  of  the  exact  size,  which  is  made  in 
halves,  and  cut  off  to  the  right  length  with  a  hot  knife.  With  any 
particular  cement  a  weighed  amount  known  to  make  a  cylinder  of 
proper  size  may  be  taken  and  rolled  to  the  right  length  instead  of 
using  a  mould. 

The  cylinders,  while  still  warm,  are  pressed  upon  the  brass 
plate  until  they  adhere  and  allowed  to  come  to  a  constant  tem- 
perature by  immersion  in  water  before  warming  for  the  flow  test. 
The  cylinders  must  stick  to  the  flow  plate  in  the  beginning  or  they 
may  slide  instead  of  flow.  The  flow  plates  are  8x2|  inches  hi 
size  and  have  corrugations  for  four  cylinders.  As  has  been  said 
the  selection  of  some  means  of  affording  a  uniform  temperature  is 
the  most  difficult  one.  In  the  New  York  Testing  Laboratory, 
a  carefully  regulated  rectangular  air  bath  illuminated  by  a 
small  incandescent  bulb  and  containing  a  mica  covered  window 
in  the  door  is  employed.  At  the  plants  a  box  heated  by  a 
<;oil  of  pipe  through  which  steam  is  conducted  can  be  arranged; 
or,  for  rough  work,  the  plate  is  placed  over  a  stove  with- 
out being  in  contact  with  the  metal.  In  trying  any  new 
method  of  heating  it  is  well  to  put  duplicates  of  the  same  material 
on  different  parts  of  the  plate  and  see  if  they  flow  alike.  This  will 
determine  whether  the  oven  is  sufficiently  uniformly  heated  for 
practical  purposes. 

Flows  of  Trinidad  asphalt  cements  are  made  at  about  160°  F., 
others  at  somewhat  lower  or  higher  temperatures,  as  the  case  may 
demand.  One  kind  of  cement  cannot,  of  course,  be  compared  with 
that  made  from  another  bitumen,  even  if  they  have  the  same  pene- 
tration at  78°  F. 

Composition  of  Asphalt  Cement. — The  percentages  of  bitumen, 
organic  insoluble  matter  and  inorganic  or  mineral  matter  in  all 
asphalt  cements  can  be  determined  exactly  as  in  refined  asphalts. 

The  naphtha  soluble  bitumen  is  sometimes  sought  with  a  view  to 


570  THE  MODERN  ASPHALT  PAVEMENT. 

its  examination  and  the  determination  of  the  nature  and  amount  of 
flux  which  has  been  used  in  making  the  cement.  .This  is  done  in  the 
same  way  as  with  refined  asphalts  or  fluxes,  but  the  naphtha 
solution  is  evaporated  and  the  residual  bitumen  examined.  Al- 
though it  will  contain  the  malthenes  of  the  asphalt  as  well  as  those 
of  the  flux  used  in  making  the  cement,  the  percentage  of  the  former 
being  known  for  any  given  asphalt,  it  is  possible  to  calculate  the 
latter  if  the  cement  has  not  been  maintained  at  a  high  temperature 
in  a  melted  state  for  too  long  a  time  with  volatilization  and  loss  of 
oil.  From  the  physical  characteristics  and  distillation  the  nature 
of  the  flux  can  generally  be  determined  as  between  an  eastern 
or  California  residuum,  and  the  presence  of  coal-tar  or  dead-oil 
is  easily  detected. 

The  bitumen  in  asphalt  cements  holding  much  organic  matter 
can  be  estimated  only  by  percolation  with  the  Gooch  crucible, 
but  in  Trinidad  and  other  cements  carrying  much  mineral  matter, 
when  examined  in  large  number,  the  bitumen  can  be  more  expedi- 
tiously  determined  by  the  centrifugal  machine.  The  centrifugal 
machine  in  use  for  this  purpose  in  the  New  York  Testing  Labora- 
tory, at  Maurer,  N.  J.,  is  a  large  Troy  laundry  extractor  with  a  bas- 
ket 30  inches  in  diameter,  which  has  been  filled  about  the  circum- 
ference with  solid  boxwood,  leaving  an  opening  11  inches  in 
diameter  in  the  centre.  In  this  boxwood  are  bored  about  three 
dozen  one-inch  holes  to  a  depth  of  6^  inches,  sloping  downward 
at  an  angle  of  15°,  provided  with  metal  liners,  in  the  bottom  of 
which  a  piece  of  sponge  is  placed  to  form  a  cushion  with  water,  and 
which  in  turn  hold  the  glass  tubes,  about  1  inch  in  exterior  diameter 
and  8  inches  long,  weighing  50  to  60  grams,  in  which,  after  being 
accurately  weighed,  is  placed  1  gram  of  the  asphalt  cement  stirred 
up  with  bisulphide  of  carbon  to  reach  to  a  height  not  greater  than 
4J  to  4J  inches  in  the  tube  and  amounting  to  30-35  c.c.  of  solvent. 
The  tubes  and  substance  thus  prepared  are  placed  in  the  centrifugal 
in  such  a  way  as  to  balance  the  basket  and  the  power  is  applied 
to  give  a  revolution  of  1500  per  minute.  This  is  kept  up  for  fifteen 
minutes,  when  the  tubes  are  taken  out  and  decanted  carefully,  with- 
out pouring  off  any  sediment  into  flint  8-ounce  wide-mouth  bottles 
labelled  with  the  same  number  as  the  tubes.  More  bisulphide  of  car- 


METHODS  OF  ANALYSIS.  571 

bon  is  then  added,  the  sediment  thoroughly  mixed  with  it  by  means 
of  an  iron  rod,  which  is  afterwards  washed  off  with  the  solvent, 
and  the  tubes  again  placed  in  Ihe  centrifugal  and  run  ten  minutes. . 
The  decanting  is  repeated  into  the  correction  bottle,  more  solvent 
added  as  before,  and  the  tubes  swung  a  third  time.  The  third 
decantation  usually  leaves  the  residue  free  from  any  amount  of 
bitumen  which  would  influence  the  results.  The  tubes  are  placed 
in  a  warm  spot  to  volatilize  the  remaining  solvent  and  when  dry 
are  weighed.  In  the  meantime  the  bisulphide  of  carbon  solution 
is  burned  for  a  correction,  as  in  the  analysis  of  refined  asphalts, 
and  the  weight  added  to  that  of  the  tube.  The  loss  of  weight  of 
the  tube  gives  the  percentage  of  bitumen  in  the  cement. 

An  excellent  power  centrifuge  holding  six  tubes  which  is 
driven  by  electricity  is  furnished  by  the  American  Name  Plate 
Company,  62  Sudbury  Street,  Boston,  Mass. 

Change  in  Consistency  of  Asphalt  Cements  on  Maintaining 
in  a  Melted  Condition. — This  change  can  be  found  by  heating  some 
of  the  cement  to  any  desired  temperature,  as  hi  the  determination 
of  loss  at  325°  F.  in  fluxes  and  making  penetrations  before  and 
after  heating. 

This  treatment,  however,  is  much  more  severe  than  any  that 
a  cement  would  ever  receive  at  a  plant,  as  the  surface,  as  com- 
pared to  the  volume  under  treatment,  is  very  much  larger  than 
is  the  case  in  a  melting-kettle  or  dipping-tank.  Such  determina- 
tions are,  in  consequence,  of  relative  value  only  in  comparing 
cements  made  with  different  fluxes. 

Mineral  Aggregate. — The  mineral  aggregate  is  determined  in 
the  same  manner  as  in  solid  bitumens. 

Examination  of  the  Finished  Surface  Mixture. — Samples  of 
surface  mixture  are  examined  as  to  the  per  cent  of  bitumen  they 
contain  and  the  grading  of  the  mineral  aggregate. 

Bitumen. — The  amount  of  bitumen  is  determined  in  one  of  two 
ways: 

1.  A  funnel,  2J  inches  in  diameter,  with  a  short  stem,  is  placed 
in  a  conical  flat-bottom  assay  flask,  holding  about  250  Q.C. 
A  Schleicher  &  Schiill  9  cm.  597  filter-paper  is  folded  and  placed  hi 
the  funnel.  Ten  grams  of  the  surface  mixture  are  weighed  out 


572  THE  MODERN  ASPHALT  PAVEMENT. 

in  fair-sized  pieces  on  the  balance  to  be  described  later  and  placed 
upon  the  filter.  With  a  washing-bottle  provided  with  two  tubes 
through  its  cork,  one  reaching  to  the  bottom  of  the  bottle  and  the 
other  only  just  passing  the  cork,  but  with  a  capillary  orifice,  a 
small  stream  of  bisulphide  of  carbon  can  be  delivered  on  inverting 
the  flask  without  the  necessity  of  using  pressure  from  the  mouth 
and  inhaling  the  noxious  vapor  of  the  solvent.  With  this  bottle 
a  fine  stream  is  directed  on  the  surface  mixture,  but  no  more  than 
it  can  absorb.  It  is  allowed  to  stand  until  it  has  softened  and 
settled  upon  the  filter.  The  latter  is  then  filled  up  to  an  eighth 
of  an  inch  below  the  rim  and  the  funnel  covered  with  a  2J-inch 
watch-glass.  It  is  not  filled  up  at  first,  as  before  the  mixture  has 
been  softened  and  settled  upon  the  paper  the  solvent  would  have 
run  through  the  filter-paper  and  would  not  have  been  used  econom- 
ically. As  the  percolation  goes  on  the  solvent  is  renewed,  and 
if  it  goes  too  slowly  the  rate  may  be  hastened  by  washing  between 
the  paper  and  the  funnel  with  bisulphide,  which  will  Dissolve  the 
bitumen,  which  may  have  hardened  and  closed  the  pores  by  evapo- 
ration, or  by  lifting  the  filter  a  little  and  letting  it  drop  back. 
On  the  day  the  analysis  is  started  the  sand  is  washed  as  clean  as 
possible,  but  nothing  more  is  done.  The  filter  with  the  sand  and 
the  percolate  is  allowed  to  stand  overnight  to  permit  anything 
that  has  run  through  to  settle  out. 

In  the  morning  the  funnel  is  placed  in  a  clean  assay  flask  and 
the  percolate  is  carefully  decanted  into  a  correction  bottle,  being 
careful  not  to  disturb  the  sediment. 

Some  bisulphide  of  carbon  is  poured  on  this,  it  is  shaken  up 
and  poured  back  on  the  filter,  the  first  assay  flask  being  thoroughly 
cleaned  with  a  feather  and  everything  brought  upon  the  original 
filter-paper.  The  mineral  aggregate  is  washed  clean  with  the  solvent. 

The  percolate,  or  solution  of  bitumen,  in  bisulphide  of  carbon 
is  poured  from  the  correction  bottle  into  a  dish,  burned,  ignited, 
and  the  correction  obtained. 

In  the  meantime  the  mineral  aggregate  after  drying  is  separated 
from  the  filter  over  a  piece  of  glazed  paper  by  scraping  with  a 
blunt  spatula  or  rubbing  between  the  fingers  in  an  appropriate  way 
until  all  the  mineral  matter  that  can  be  removed  is  separated, 


METHODS  OF  ANALYSIS.  573 

taking  care,  of  course,  not  to  detach  any  fibres  of  the  paper.  It 
is  then  dusted  into  a  weighed  No.  2  Royal  Berlin  porcelain  cnicible 
and  set  aside.  The  filter-paper,  containing  much  fine  mineral 
matter  in  its  pores,  is  burned  either  with  the  correction  in  its  dish 
or  in  any  satisfactory  way,  its  ash  and  the  correction  added  to  the 
mineral  aggregate  and  the  crucible's  entire  contents,  after  one 
is  assured  that  no  trace  of  solvent  remains,  is  weighed.  The 
difference  in  the  weight  of  the  aggregate  and  the  ten  grams  of 
surface  taken  is  that  of  the  bitumen  and  gives  the  per  cent  of 
bitumen  in  the  mixture,  which  should  be  calculated  to  the  nearest 
tenth  of  one  per  cent.  The  expression  of  the  percentage  in  hun- 
dredths  is  beyond  the  limit  of  accuracy  of  the  method  and  is 
cumbersome  and  unnecessary. 

Centrifugal  Method  for  the  Examination  of  Surface  Mix- 
ture.— In  laboratories  where  large  numbers  of  surface  mixtures 
are  examined  daily,  as  in  that  of  the  author,  where  the  number 
has  reached  70,  the  centrifugal  method  as  described  on  page  570 
is  commonly  used.  Ten  grams  of  the  surface  mixture  are  weighed 
out  in  a  glass  tube  and  submitted  to  the  same  treatment  as  is 
applied  to  asphalt  cements.  The  loss  of  weight  of  the  tube  minus 
that  of  the  correction  obtained  on  burning  the  extracted  bitumen 
gives  the  percentage  of  bitumen  in  the  mixture.  Should  the 
mineral  aggregate  contain  coal  or  other  material  too  light  to 
be  thrown  out  by  centrifugal  action,  the  decanted  bisulphide 
must  be  filtered  before  burning  or  the  percolation  method  alone 
can  be  used. 

Grading  of  the  Mineral  Aggregate  in  a  Surface  Mixture.— The 
mineral  aggregate  from  the  porcelain  crucible  after  having  been 
weighed  for  the  determination  of  bitumen  or  the  mineral  matter 
from  the  glass  tube  which  has  been  submitted  to  the  centrifugal 
process  is  emptied  upon  the  200-mesh  sieve.  The  particles  of 
dust,  which  are  caked  together,  are  broken  up  by  gentle  pressure 
with  the  finger  tips  and  the  coarser  sand  grains  thoroughly  cleaned 
by  attrition.  When  nothing  further  passes  the  sieve  the  residue 
is  transferred  hi  any  convenient  way  to  the  pan  of  a  balance, 
preferably  one  which,  while  weighing  accurately  to  a  hundredth 
of  a  gram  or  one-tenth  per  cent  of  the  amount  of  surface  mixture 


574 


THE  MODERN  ASPHALT  PAVEMENT. 


taken,  does  not  require  the  use  of  weights  but  can  be  rapidly 
manipulated. 

Such  a  balance  is  supplied  by  the  C.  H.  Stoelting  Co.,  31  W. 
Randolph  St.,  Chicago,  111.,  or  Eimer  &  Amend,  New  York,  in  the 
Chaslyn  balance,  Fig.  39.  This  is  a  beam  balance,  very  much  of 
the  Westphal  specific  gravity  type,  which  weighs  readily  to  10  m^s. 
by  moving  ring.?  of  different  weight  along  the  beam.  It  is  exactly 
suited  for  rapid  work  with  surface  mixtures  where  results  no  closer 
than  iV  of  1  per  cent  are  sought.  With  this  balance  the  weight 


FIG.  39. — Chaslyn  Balance. 

of  the  residue  on  the  200-mesh  sieve  is  obtained  and  the  differ- 
ence between  this  and  the  weight  of  the  mineral  aggregate  gives  the 
percentage  of  200-mesh  material  and  filler  in  surface  mixture.  It  is 
a  determination  by  loss,  and  so  no  effort  is  necessary  to  save  the 
dust  which  passes  the  sieve,  unless  it  is  desired  tc  determine  its 
chemical  nature  or  subdivide  further  by  elutriation  when  it 
should  be  caught  in  a  closely  fitting  pan. 


METHODS    OF    ANALYSIS. 


575 


The  other  sieves  are  used  in  succession  after  the  200-mesh 
with  the  precautions  mentioned  under  sands  and  the  percentages 
passed  by  each  determined. 

The  percentage  of  bitumen,  dust,  or  filler,  and  various  sized 
sand  should  amount  to  100  per  cent. 

The  results  are  reported  on  the  following  form: 

NEW  YORK  TESTING  LABORATORY, 

MAURER,  N.  J., 

Mesh  composition  and  quality  of 

Received  from . . 


Test  No. 
Test  No. 
Test  No. 
Test  No . 


Sample  No. 
Sample  No. 
Sample  No. 
Sample  No. 


Test  No. 

Standard  Mixture. 

Per  Cent. 

Per  Cent. 

Per  Cent. 

PerCent. 

Heavy 
Traffic 

Light 
Traffic 

No. 

Pass- 
ing 

Total 

Pass- 
ing 

Total 

Pass- 
ing 

Total 

Pass- 
ing 

Total 

10.5 

10.0 

Bit. 

13.0 

10.0 

200 

13.0\9ft  n 
13.  0/260 

J18.0 

100 
80 

24.0 

50 

11.0 

40 

8.0] 

] 

30 

5.0[16  0 

^24.0 

20 

3.0J 

J 

10 

On 

10 

Penetration  of  A.  C. 

Pat  paper  stain.  . . . 

Remarks: 


576  THE   MODERN    ASPHALT   PAVEMENT. 

Method  for  the  Examination  of  Asphaltic  Concrete  and  As- 
phalt Blocks. — The  quantity  of  concrete  which  should  be  taken 
for  the  analysis  will  depend  upon  the  size  of  the  largest  particles 
of  the  mineral  aggregate. 

Three  hundred  grams  of  an  asphalt  block,  500  grams  when 
the  largest  particles  range  from  ^  to  J  inch,  or  1000  grams  when 
1  inch  particles  predominate,  will  be  sufficient.  Several  com- 
parative analyses  of  the  latter  class,  employing  respectively,  1, 
2,  and  10  kilos  of  the  sample,  were  in  very  close  agreement. 

In  order  to  retain  the  original  relation  of  the  various  particles 
of  the  mineral  aggregate,  it  is  obvious  that  none  of  the  stones 
should  be  fractured  in  taking  the  portion  for  analysis,  and  the 
sample  should  accordingly  be  softened  by  heating  so  that  it  may 
readily  be  broken  apart  by  hand. 

Analysis  by  Decantation. — An  appropriate  amount  of  the 
sample  is  placed  in  a  metal  beaker  or  measure,  covered  with 
carbon  disulphide  and  allowed  to  settle  for  two  hours;  decant 
and  cover  with  fresh  carbon  disulphide;  repeat  this  treatment 
until  the  solution  becomes  clear. 

Burn  off  the  carbon  disulphide  to  recover  the  mineral  matter 
carried  over  with  the  extract,  in  a  platinum  or  porcelain  dish. 
Dry  and  weigh  residue  together  with  the  correction.  The  loss 
from  weight  of  concrete  taken  is  bitumen. 

The  mineral  aggregate  may  now  be  further  examined  by  care- 
fully compacting  in  a  suitable  vessel  to  determine  the  amount 
of  voids  or  sifted  through  a  series  of  perforated  metal  and  wire 
cloth  screens  to  ascertain  the  size  of  the  various  particles  or  its 
grading. 

Centrifugal  Method. — While  the  preceding  method  is  not  lack- 
ing in  accuracy,  when  intelligently  manipulated,  it  is  far  from 
rapid,  especially  when  a  large  mass  of  material  is  under  considera- 
tion, and  more  or  less  extravagant  in  the  use  of  solvent.  The 
following  method  has  therefore  been  developed,  applying  the 
essentials  of  the  special  centrifugal  extractor  as  closely  as  they 
could  be  gathered  from  a  brief  verbal  description,  very  kindly 
supplied  by  its  ingenious  inventor,  Mr.  August  E.  Shutte. 

The  body  of  the  apparatus  consists  of  a  double  walled  iron 


METHODS    OF    ANALYSIS. 


577 


casting,  the  inside  dimensions  of  which  are  9^  inches  diameter  by 
7  inches  deep,  set  upon  three  legs  and  provided  with  a  tightly 
fitting  cover  carrying  a  reservoir,  also  consisting  of  a  single  cast- 
ing. The  combined  portions  form  in  effect  a  large  Soxhlet 
extractor,  as  will  be  observed  upon  inspection  of  the  illustrations, 
Figs.  40  and  41. 


FIG.  4«. 


A  slotted  shaft  extends  through  the  bottom  of  the  extractor 
and  a  gland  is  provided  for  making  a  tight  joint.  This,  as  well  as 
the  gasket  under  the  cover,  may  be  packed  with  ball  lamp  wicking 
and  soap. 

The  sample  is  broken  down  as  finely  as  practicable  and  placed  on 


578 


THE    MODERN    ASPHALT    PAVEMENT. 


the  cast  iron  plate  which  fits  upon  the  end  of  the  slotted  shaft.     A 
filter  ring  cut  from  No.  80  soft  roofing  felt  about  .090  inches  thick 


. 


FIG.  41. 

is  placed  under  the  rim  of  the  dome,  which  is  now  bolted  down 
hard  upon  the  plate  over  the  sample.     Fig.  42. 

A  dome  8  inches  diameter  by  3^  inches  high,  spun  out  of  No.  16 
brass,  will  accommodate  one  kilogram  of  concrete.     The  plate  is 


METHODS    OF     ANALYSIS. 


579 


Si  inches  diameter.  The  bolt  should  be  tool  steel,  -^  inch 
diameter.  A  shallow  brass  pan  is  placed  in  the  device  to  receive 
the  extract  as  it  is  thrown  out  of  the  revolving  dome. 

The  dome  having  been  placed  in  position  upon  the  shaft,  about 
300  cc.  carbon  disulphide  is  poured  upon  the  sample  through  the 
perforations  in  the  top  and  the  apparatus  closed. 

Steam  is  turned  into  the  lower  jacketed  bod}'  and  cold  water 
through  the  condenser.  After  allowing  a  few  minutes  to  become 
warm,  the  dome  is  revolved  at  a  rate  of  from  1500  to  1800  R.  P.  M. 
by  any  suitable  power,  and  as  the  solvent  carrying  the  bitumen 
is  thrown  out  into  the  receiving  pan,  it  is  volatilized  and  passes  into 


FIG.  42. 

the  reflux  condenser,  falling  back  into  the  reservoir  on  the  cover. 
AVhen  about  250  cc.  has  accumulated,  it  is  automatically  syphoned 
back  into  the  dome  upon  the  sample  as  fresh  solvent. 

As  but  three  minutes  are  required  to  swing  the  sample  dry, 
it  is  not  necessary  to  revolve  the  dome  continuously;  stop  it  after 
this  period  of  time  and  do  not  start  again  until  the  gauge  glass  on 
the  reservoir  indicates  that  a  fresh  portion  of  solvent  has  passed 
over  upon  the  sample. 

About  four  treatments  are  sufficient  for  a  kilogram  sample, 
after  which  the  flow  of  steam  is  discontinued  and  cold  water  re- 
versed through  the  jacket  to  hasten  cooling. 


580  THE  MODERN  ASPHALT  PAVEMENT^ 

The  bitumen  free  from  all  but  minute  traces  of  the  finest  portion 
of  the  mineral  aggregate,  which  may  be  disregarded,  will  be  found 
in  the  pan,  while  the  clean  aggregate  is  allowed  to  dry  spontane- 
ously and  then  weighed,  the  bitumen  being  determined  by  dif- 
ference. It  is  examined  further  as  desired,  by  sifting,  etc.,  as 
previously  described. 

The  entire  extraction  may  thus  readily  be  completed  in  less 
than  an  hour,  with  little  loss  of  solvent. 

In  handling  asphalt  block  mixtures  employing  300  grams  of 
sample  and  but  three  portions  of  cold  carbon  disulphide,  an  ex- 
traction may  be  made  in  about  twenty  minutes.  In  the  latter 
case,  the  solvent  is  recovered  in  a  separate  distilling  apparatus 
arranged  to  receive  the  pan  holding  the  extract  directly,  or  an 
accumulation  is  worked  over  at  convenient  times. 

Density  and  Voids  in  Surface  Mixtures. — The  density  which 
a  surface  mixture  can  attain  on  compaction  is  often  a  source  of 
information  as  to  its  quality,  and  from  this  the  voids  in  the  com- 
pacted material  can  be  calculated.  The  mixture  is  compressed 
in  a  mould  made  for  the  purpose.  This  should  consist  of  a  base 
8  inches  long,  5  inches  wide  and  3|  inches  high.  On  top  of  this 
base  are  found  a  cylindrical  boss  or  post  1J  inches  in  diameter 
and  1  inch  high,  and  a  hole  of  the  same  or  a  little  larger  diameter, 
opening  into  a  hollow  in  the  base.  A  hollow  cylindrical  mould 
or  sleeve  of  steel  of  the  same  internal  diameter  as  the  boss  and 
3J  inches  high  is  provided  and  a  solid  plunger  of  steel  to  fit  this 

accurately.  About grams  of  the  surface  mixture  is  heated 

in  a  deep  iron  dish  to  325°  F.,  the  cylinder  and  plunger  being  also 
heated.  The  cylinder  is  placed  over  the  post  and  filled  with  the 
hot  mixture  and  compressed  with  the  plunger  and  sharp  blows  of 
a  heavy  hammer,  or  better  in  any  suitable  press  such  as  the 
Riehle  or  Olsen  tensile  and  crushing  power  machines.  When 
ultimate  compression  has  been  attained  in  this  way  the  cylindrical 
mould  is  removed  from  the  boss  and  turned  over  or  reversed  and 
again  placed  on  the  boss.  The  space  formerly  occupied  by  the  boss 
now  gives  an  opportunity  for  the  insertion  of  the  plunger  and 
compression  of  the  cylinder  of  asphalt  mixture  from  the  other 


METHODS  OF  ANALYSIS.  581 

end.  Finally,  the  mould  is  placed  over  the  opening  in  the  base 
and  the  cylinder  of  surface  knocked  out  with  a  few  blows  of  the 
plunger.  It  should  be  between  1  and  2  inches  long. 

Its  density  can  be  determined  by  weighing  it  in  air  and  water, 
but  the  quickest  way  is  to  measure  its  length  with  calipers  to  .01 
inch  and  find  its  volume  in  cubic  centimeters  by  reference  to  the 
table  on  page  582. 

The  weight  of  the  cylinder  divided  by  the  volume  gives  the 
density.  This  should  not  fall  below  2.20  for  good  mixtures,  made 
with  quartz  sand.  The  voids  in  such  a  cylinder  can  be  calculated 
from  the  known  proportions  and  density  of  the  materials  of  which 
it  is  composed,  as  can  be  seen  from  the  following  example: 

The  customary  surface  mixtures  consist,  in  parts  by  weight,  of: 

Sand 75% 

Dust 10 

Trinidad  asphalt  cement 15 

100% 

By  volume  this  would  be,  the  density  of  the  sand  being  2.65,  that 
of  dust  2.60,  and  that  of  the  asphalt  cement  1.25: 

Sand 75/2  65...   28.30    or       64.10 

Dust 10/2.60...     3.85     "          8.72 

Asphalt  cement..  15/1. 25...   12.00     "       27.18 

44.15  100.00 

The  cement  in  use,  being  27. 18%  of  the  entire  volume  of  the  mix- 
ture, will  fill  the  voids  which  ordinarily  exist  in  the  mineral  aggregate 
if  the  mixture  receives  its  ultimate  compression  and  density.  If 
the  voids  are  larger  it  will  be  too  little  and  some  voids  will  remain 
unfilled;  if  they  are  smaller  it  will  be  too  much  and  will  make  the 
surface  too  yielding. 

Considering  the  proportions  given  as  being  theoretically  cor- 
rect, the  density  of  the  resulting  mixture,  when  it  receives  its 
ultimate  compression,  should  be: 

64 . 1  vols.  at  2 . 65  density 1 . 699 

8.7     "     "  2.60       "      226 

27.2  "     "  1.25      "  .340 


100.0  2.265 


582 


THE  MODERN  ASPHALT  PAVEMENT. 


TABLE  FOR  DETERMINING  CONTENTS  IN  CUBIC  CENTIMETERS 
OF  CYLINDERS  1.25  INCHES  IN  DIAMETER  AND  VARIOUS 
HEIGHTS  IN  INCHES. 


Height, 
Inches. 

Cubic 
Inches. 

Cubic 
Centimeters. 

!        Height, 
Inches. 

Cubic 
Inches. 

Cubic 
Centimeters. 

.95 

1.17 

18.17 

.48 

1.81 

29.66 

.96 

1.18 

19.34 

.49 

1.83 

29.99 

.97 

1.19 

19.50 

.50 

1.84 

30.15 

.98 

1.20 

19.66 

.51 

1.85 

30.32 

.99 

1.22 

19.99 

.52 

1.86 

30.48 

.00 

1.23 

20.16 

.53 

1.87 

30.64 

.01 

.24 

20.32 

.54 

1.89 

30.97 

.02 

.25 

20.48 

.55 

1.90 

31.14 

.03 

.26 

20.65 

.56 

1.91 

31.30 

.04 

.28 

20.98 

.57 

1.93 

31.63 

.05 

.29 

21.14 

.58 

1.94 

31.79 

.06 

.30 

21.30 

.59 

1.95 

31.95 

.07 

.31 

21.47 

.60 

1.96 

32.12 

.08 

.33 

21.79 

.61 

1.98 

32.45 

.09 

.34 

21.96 

.62 

1.99 

32.61 

1.10 

.35 

22.12 

.63 

2.00 

32.77 

1.11 

.36 

22.28 

.64 

2.01 

32.94 

1.12 

.37 

22.45 

.65 

2.02 

33.09 

.13 

.39 

22.78 

.66 

2.04. 

33.42 

.14 

.40 

22.94 

.67 

2.05 

33.59 

.15 

.41 

23.11 

.68 

2.06 

33.76 

.16 

.42 

23.27 

.69 

2.07 

33.92 

.17 

.44 

23.60 

.70 

2.09 

34.25 

.18 

.45 

23.76 

.71 

2.10 

34.41 

.19 

.46 

23.92 

.72 

2.11 

34.58 

.20 

.47 

24.08 

.73 

2  12 

34.74 

.21 

1.48 

24.25 

1.74 

2'l4 

35.07 

.22 

1.50 

24.58 

1.75 

2.15 

35.23 

.23 

1.51 

24.74 

1.76 

2.16 

35.40 

.24 

1.52 

24.91 

1.77 

2.17 

35.56 

.25 

1.53 

25.07 

1.78 

2.19 

35.89 

.26 

1.55 

25.40 

1.79 

2.20 

36.05 

.27 

1.56 

25.56 

1.80 

2.21 

36.21 

.28 

1.57 

25.73 

.81 

2.22 

36.38 

.29 

1.58 

25.89 

.82 

2.23 

36.54 

.30 

1.60 

26.22 

.83 

2.25 

36.87 

.31 

1.61 

26.38 

.84 

2.26 

37.03 

1.32 

1.62 

26.55 

.85 

2.27 

37  20 

1.33 

1.63 

26.71 

.86 

2.28 

37.36 

1.34 

1.65 

27.04 

1.87 

2.29 

37.53 

.35 

1.66 

27.20 

1.88 

2.31 

37.85 

.36 

1.67 

27.35 

1.89 

2.32 

38.02 

.37 

1.68 

27.53 

1.90 

2.33 

38.18 

.38 

1.69 

27.69 

1.91 

2.34 

38.35 

.39 

1.70 

27.86 

1.92 

2.36 

38.67 

.40 

1.72 

28.18 

1.93 

2.37 

38.84 

.41 

1.73 

28.35 

1.94 

2.38 

39.00 

.42 

1.74 

28.51 

1.95 

2.39 

39.16 

1.43 

1.75 

28.68 

1.96 

2.41 

39.49 

1.44 

1.77 

29.00 

1.97 

2.42 

39.66 

1.45 

1.78 

29.17 

1.98 

2.43 

39.82 

1.46 

1.79 

29.33 

1.99 

2.44 

39.98 

1.47 

1.80 

29.50 

I        2.00 

2.45 

40.15 

METHODS    OF    ANALYSIS.  583 

The  density  of  the  compacted  mixture  is  usually  found  to  be  not 
over  2.22,  and  at  this  figure  there  would  be  about  2  per  cent  of 
voids.  At  a  density  of  2.18  the  voids  would  reach  3.7  per  cent. 

The  density  of  coarse  mixtures,  such  as  asphalt  blocks  or  as- 
phaltic  concrete,  may  be  determined  by  compressing  the  hot 
mixture  in  a  mold  of  appropriate  size  under  suitable  pressure  in  a 
power  press. 

Asphalt  blocks  are  weighed  as  received,  first  in  air  and  then 
in  water,  in  the  most  convenient  manner,  and  the  density  cal- 
culated from  the  data  thus  obtained. 

The  specific  gravity  of  the  mineral  aggregate  in  such  mixtures 
is  most  conveniently  determined  in  a  Jackson's  apparatus,  pre- 
viously referred  to. 

Water  Absorption  of  Surface  Mixtures. — Cylinders  prepared  as 
previously  described,  or,  if  such  a  mould  is  not  at  hand,  compressed 
to  the  best  possible  extent  in  an  ordinary  diamond  mortar,  are 
weighed  in  air  and  then  suspended  by  a  horsehair  and  immersed 
in  distilled  water  at  ordinary  temperature  and  again  weighed,  while 
still  immersed  in  water  and  suspended  by  the  hair  in  the  same 
way,  at  intervals  of  1,  2,  7,  15  days  and  one  month.  The  gain  in 
weight  shows  the  water  absorbed,  which  is  calculated  to  milligrams 
per  square  centimeter,  or  inch,  or  pounds  per  square  yard,  as  may 
be  desired,  by  determining  from  its  dimensions  the  number  of 
square  inches  of  surface  the  cylinder  has. 

Where  cylinders  are  of  such  density  that  the  surface  is  but  slightly 
acted  upon  by  water  and  there  is  no  disintegration,  they  may  be 
carefulty  wiped  off  and  weighed  directly. 

An  example  of  the  amount  of  water  absorbed  by  a  good  mix- 
ture is  seen  in  the  following  determinations: 


584 


THE    MODERN    ASPHALT    PAVEMENT. 


GAIN  IN  GRAMS  PER  SQUARE  INCH  AND  POUNDS  PER  SQUARE 
YARD  OF  TRINIDAD  SURFACE  MIXTURE  FROM  THE  LONG 
ISLAND  CITY  PLANT  OF  THE  BARBER  ASPHALT  PAVING 
COMPANY. 

Height  of  cylinder 1.15  inches 

Diameter 1 . 25      " 

Surface 6 . 97  square  inches 


Interval 

Mgs.  Per  Square  Inch. 

Pounds  Per 
Square  Yard. 

After 

Immersion. 

Gain  in 

Total 

Total 

Interval. 

Gain. 

Gain. 

24  hours 

.0169 

48       " 

.0021 

.0190 

.0540 

7  days 

.0092 

.0282 

.0803 

15      " 

.0045 

.0327 

.0930 

28      " 

.0935 

.0362 

.  1031  » 

See  also  pages  465  and  468. 


TABLE  FOR  DETERMINING  SQUARE  INCHES  OF  SURFACE  IN 
CYLINDERS  1.25  INCHES  IN  DIAMETER  AND  VARIOUS 
HEIGHTS  IN  INCHES. 


Height. 

Square 
Inches. 

Height. 

Square 
Inches. 

Height. 

Square 
Inches. 

1.00 

6.38 

1.28 

7.48 

1.65 

8.93 

1.10 

6.77 

1.30 

7.56 

1.68 

9.05 

1.11 

6.81 

1.33 

7.68 

1.70 

9.13 

.12 

6.85 

1.35 

7.76 

1.73 

9.25 

.13 

6.89 

1.38 

7.87 

1.75 

9.33 

.14 

6.93 

.40 

7.95 

1.78 

9.45 

.15 

6.97 

.43 

8.07 

1.80 

9.52 

.16 

7.01 

.45 

8.15 

.83 

9.64 

.      .17 

7.05 

.48 

8.27 

.85 

9.72 

.18 

7-.  08 

.50 

8.34 

.88 

9.84 

.19 

7.13 

1.53 

8.46 

.90 

9.92 

.20 

7.17 

1.55 

8.54 

.93 

10.03 

.21 

7.21 

1.58 

8.66 

.95 

10.11 

.22 

7.24 

1.60 

8.74 

.98 

10.23 

.25 

7.36 

1.63 

8.86 

2.00 

10.31 

Weight  of  water  m  pounds 

~ — = ^ — r. — : — : : — : — X  2.85 =pounds  absorbed  per  square  yard. 

Surface  of  cylinder  m  square  inches 


METHODS   OF    ANALYSIS.  585 

Other  Physical  Tests. — Other  physical  tests  of  surface  mixtures 
are  made  at  times,  such  as  determination  of  tensile  and  compression 
strength,  shearing  tests,  ductility  of  cements  at  various  tempera- 
tures, abrasion,  etc.,  but  as  they  are  only  done  for  special  purposes 
they  need  not  be  described  here.  It  may  be  said,  however,  that 
it  should  be  possible  to  rub  together  wet  cylinders  of  any  mixture 
without  detaching  particles  of  the  mineral  aggregate,  and  that  if 
this  cannot  be  done  such  a  mixture  will  not  be  capable  of  with- 
standing cold,  wet  weather. 

Old  Street  Surfaces. — Old  street  surfaces  are  frequently  examined 
to  determine  their  composition,  the  percentage  of  bitumen  and 
the  grading  of  the  mineral  aggregate,  the  consistency  of  the  bitumen 
they  contain,  their  density  and  their  power  to  resist  water.  All 
these  determinations  are  made  according  to  methods  already 
described  with  almost  no  modifications  except  that  the  material 
should  be  carefully  dried.  Enough  surface  mixture  is  extracted 
alongside  a  standard  check  cement  to  furnish  the  same  amount 
of  bitumen,  a  piece  of  surface  is  shaped  to  such  a  form  for 
the  water  absorption  test  that  its  superficial  area  can  be  calcula- 
ted and  the  nature  of  the  aggregate,  sand  and  filler,  may  be  as 
carefully  examined  as  a  new  mixture  made  with  known  materials. 

Determination  of  the  Consistency  of  the  Bitumen  in  Paving 
Mixtures. — Where  no  sample  of  the  asphalt  cement  which  has 
been  used  in  making  a  surface  mixture  is  available  for  the  determina- 
tion of  its  consistency  this  can  be  arrived  at  very  closely  by  proceed- 
ing as  directed  for  the  preparation  of  pure  bitumen  on  page  547. 

Modification  of  Methods. — The  preceding  methods  are  such  as 
are  in  use  in  the  paving  industry  at  the  present  time;  but  they 
are,  of  course,  subject  to  change  and  improvement  from  time  to 
time. 

Impact  Tests  for  Toughness  of  Asphalt  Surface  Mixture. — This 
test  is  made  with  the  machine  devised  for  the  purpose  of  testing  the 
toughness  of  rocks  by  Mr.  Logan  Waller  Page,  of  the  Office  of  Public 
Roads,  U.S.  Department  of  Agriculture,  and  described  in  Bulletin  No. 
79,  Bureau  of  Chemistry,  U.  S.  Department  of  Agriculture,  page 
33,  on  cylinders  1J  inches  in  diameter  and  1  inch  high  and  weighing 
about  50  grams.  The  cylinders  are  prepared  by  compressing 


586  THE   MODERN    ASPHALT    PAVEMENT. 

sufficient  of  the  hot  surface  mixture,  at  an  appropriate  tempe^a- 
ture,  in  the  steel  mould  previously  described  for  the  preparation 
of  test  pieces  for  density.  In  this  way  a  density  of  the  cylinder 
from  2.2  to  2.3  can  readily  be  attained.  When  the  cylinders  are 
cooled  they  are  brought  to  a  normal  temperature  of  40,  78,  and 
100°  F.,  and  tested  to  the  breaking  point  in  the  machine,  that 
mixture  being,  of  course,  the  toughest  which  withstands  the  most 
blows. 

Mr.  Page  describes  the  manner  of  making  the  test  as  follows: 
"This  test  is  made  on  cylinders  with  an  impact  machine 
especially  designed  for  the  purpose.  Instead  of  a  flat  end  plunger 
resting  on  the  test-piece  as  in  the  cementation  test,  a  plunger 
with  the  lower  and  bearing  -surface  of  spherical  shape,  having 
a  radius  of  1  cm.  (0.4  inch)  is  used.  It  can  be  seen  that  the  blow 
as  delivered  through  a  spherical-end  plunger  approximates  as 
nearly  as  practicable  the  blows  of  traffic.  Besides  this,  it  has 
the  further  advantage  of  not  requiring  great  exactness  in  getting 
the  two  bearing  surfaces  of  the  test-piece  parallel,  as  the  entire 
load  is  applied  at  one  point  on  the  upper  surface.  The  test-piece 
is  adjusted  so  that  the  center  of  its  upper  surface  is  tangent  to 
the  spherical  end  of  the  plunger,  and  the  plunger  is  pressed  firmly 
upon  the  test-piece  by  two  spiral  springs  which  surround  the 
plunger  guide-rods.  The  test-piece  is  held  to  the  base  of  the 
machine  by  a  device  which  prevents  its  rebounding  when  a  blow 
is  struck  by  the  hammer.  The  hammer  weighs  2  kg.  and  is  raised 
by  a  sprocket  chain  and  released  automatically  by  a  concentric- 
electromagnet.  The  test  consists  of  a  1  cm.  fall  of  the  hammer 
for  the  first  blow,  and  an  increase  fall  of  1  cm.  for  each  succeed- 
ing blow  until  failure  of  the  test-piece  occurs.  The  number  of 
blows  required  to  destroy  the  test-piece  is  used  to  represent  the 
toughness." 

Indentification  of  Bitumens. — It  is  often  necessary  to  identify 
the  source  of  a  solid  bitumen  or  of  a  flux,  or  of  a  mixture  of  two 
or  more  of  these.  In  order  to  accomplish  this  a  complete  deter- 
mination of  the  physical  characteristics  and  proximate  chemical 
composition  of  the  bitumen  should  be  first  carried  out.  If  the 
data  thus  obtained  are  not  such  as  to  identify  the  material,  espe- 


METHODS    OF    ANALYSIS.  587 

cially  in  the  case  of  asphalt  cements,  an  examination  of  the  character 
of  the  mineral  matter  that  is  present  may  assist  in  forming  an 
opinion  in  regard  to  the  origin  of  the  solid  bitumen  that  is  present, 
the  ash  being  more  or  less  characteristic  of  the  source  from  which 
the  bitumen  is  derived.  For  example,  the  ash  in  Trinidad  asphalt 
is  characterized  by  a  light  p,ink  color  and,  on  microscopic  exami- 
nation, is  found  to  contain  very  sharp  particles  of  quartz  with 
fine  clay  colored  by  the  oxide  of  iron  which  is  present.  If  an  ash 
of  this  description  is  not  detected  it  will  be  safe  to  say  that  the 
material  contains  no  Trinidad  asphalt.  Some  Cuban  asphalts 
have  a  somewhat  similar  ash,  but  confusion  cannot  arise  if  they 
are  compared  microscopically  with  one  obtained  from  a  known 
sample  of  Trinidad  asphalt. 

If  the  extremely  fine  mineral  matter  which  remains  in  suspen- 
sion in  carbon  disulphide,  which  is  obtained  in  a  correction  in 
the  course  of  analysis,  is  examined,  this  will  also  be  found  to  be 
characteristic. 

If  the  bitumen  under  examination  contains  but  a  small  per- 
centage of  ash  and  this  consists  of  not  excessively  fine  mineral 
particles,  it  may  be  assumed  that  a  solid  native  bitumen  is  present 
and  that  the  material  is  not  composed  entirely  of  a  residual  pitch. 
The  residual  pitches  yield  but  traces  of  mineral  matter  and  this 
is  extremely  fine,  usually  ferruginous,  and  derived  from  the  stills 
in  which  the  distillation  has  been  carried  on. 

Gilsonite  is  so  extremely  pure  that  its  mineral  matter  can  only 
be  differentiated  from  that  of  residual  pitch  from  the  fact  that  it 
is  not  so  red  in  color. 

The  fixed  carbon  which  the  bitumen  yields  on  ignition  is  a  very 
important  factor  in  fixing  its  origin.  A  very  high  percentage 
points  to  a  grahamite.  The  residual  pitch  from  Texas  oil  yields 
more  fixed  carbon  than  those  from  California  oils.  The  asphalts, 
generally,  yield  from  10  to  15  per  cent  of  fixed  carbon.  The  fixed 
carbon  yielded  by  asphalt  cements  may  be  compared  with  that  of 
cements  of  known  origin. 

The  proportion  of  the  bitumen  soluble  in  88°  naphtha  which  is 
attacked  by  sulphuric  acid,  according  to  the  method  which  has 
been  described,  will  differentiate  bitumens  such  as  gilsonite  and 


588  THE    MODERN    ASPHALT    PAVEMENT. 

mixtures  containing  large  proportions  of  it  from  those  made  with 
asphalts.  The  same  determination  will  differentiate  the  California 
fluxes  from  those  made  from  Texas  oil,  although  this  may  be  gen- 
erally arrived  at  from  the  difference  of  the  specific  gravity  of  the 
two  materials  and  by  the  fact  that  the  Texas  oil  contains  about 
one  per  cent  of  paraffine  scale. 

Otner  determinations  which  have  been  made  in  the  course 
of  the  general  analysis  will  have  their  value  in  special  cases,  and  the 
methods  may  be  applied  according  to  the  judgment  of  the  analyst. 

It  may  be  noted  that  none  of  the  true  asphalts  contain  bitumen 
insoluble  in  cold  carbon  tetrachloride  which  is  soluble  in  carbon 
disulphide. 


CHAPTER   XXIX. 


SOLVENTS. 

BITUMEN,  as  has  appeared  in  the  preceding  pages,  is  entirely 
or  partially  dissolved  by  very  many  solvents,  and  the  relative 
solubility  in  the  different  ones  has  been  used  as  a  means  of  differ- 
entiating them.  Analysts  are  not,  however,  agreed  as  to  the  most 
suitable  solvents  to  use  for  this  purpose. 

For  the  determination  of  total  bitumen  bisulphide  of  carbon  is 
generally  employed,  but  chloroform  and  oil  of  turpentine  have  also 
been  used  for  this  purpose.  One  analyst  uses  naphtha  of  74° 
B.,  boiling  between  40°  and  60°  C.,  another  both  88°  and  62°  B. 
naphtha;  while  others  have  used  acetone  and  ethyl  ether  as  solvent 
for  the  malthenes.  It  is  of  interest  to  determine  what  there  is  in 
favor  of  the  different  solvents  and  what  there  is  against  them. 

Chloroform. — Chloroform  is  a  most  excellent  solvent  for  bitu- 
men and  might,  perhaps,  be  used  for  making  the  determination 
of  total  bitumen  were  it  not  for  certain  disadvantages.  In  a  pure 
form  it  is  extremely  expensive,  costing  $1.00  per  pound.  Commer- 
cial chloroform  is  not  sufficiently  pure  to  be  used  as  a  solvent,  as 
can  be  seen  from  the  following  determinations : 

BOILING-POINT. 


Temperature. 

Per  Cent  Distillate. 

Pure  chloroform 

61    2°  C 

f  

55°  to  60°  C. 

5  7% 

Commercial  chloroform  -I  

60°  "  62°  C. 

92  9 

Residue 

1  4 

100.0 

589 


590  THE   MODERN    ASPHALT    PAVEMENT. 

From  these  figures  it  is  evident  that  the  commercial  chloro- 
form contains  at  least  10  per  cent  of  impurities,  the  amount  of 
which  is  not  constant,  and  it  is,  therefore,  not  suitable  for  use  as  a 
solvent  for  bitumen.  Chloroform  possesses  the  additional  disad- 
vantage of  evaporating  much  moreslowlythanbisulphide  of  carbon; 
and,  as  it  is  non-inflammable,  it  cannot  be  burned  off  rapidly 
in  determining  the  correction  for  the  mineral  matter,  as  is  the  case 
with  bisulphide  of  carbon.  For  these  reasons  it  is  not  probable 
that  it  will  ever  be  adopted  as  a  standard  solvent. 

Oil  of  Turpentine. — Oil  of  turpentine  is  not  a  definite  compound. 
It  boils  between  97°  and  160°  C.,  the  greater  portion  passing  over 
between  155°  and  160°  C.  It  is  an  artificial  product,  having  no 
constant  composition,  and  is,  therefore,  unsuitable  for  use  as  a  stand- 
ard solvent. 

Bisulphide  of  Carbon. — Bisulphide  of  carbon  for  many  reasons  is 
the  best  solvent  for  the  determination  of  total  bitumen.  Objec- 
tion has  been  raised  against  it  because  a  slight  amount  of  bitumen, 
which  is  dissolved  by  chloroform  and  turpentine,  is  not  soluble 
in  it,  but  for  technical  work  at  least  it  is  entirely  satisfactory. 
It  possesses  the  great  advantage  that,  if  redistilled,  it  is  very  pure, 
with  a  constant  boiling-point  of  46°  C.  and  specific  gravity  1.27. 
It  is  the  cheapest  solvent  for  total  bitumen  that  is  available,  as  it 
can  be  brought  in  thousand-pound  lots  at  six  cents  per  pound  or 
practically  free  from  sulphur  at  8  cents,  and  it  has  not  been  found 
necessary  for  ordinary  bitumen  determinations  to  redistil  this 
material.  It  will  undoubtedly  be  adopted  as  the  standard  solvent 
for  the  purpose  for  which  it  is  used. 

Carbon  Tetrachloride. — For  the  asphalts  and  some  of  the 
native  bitumens  carbon  tetrachloride  may  be  substituted  for 
bisulpide  of  carbon;  but, as  has  appeared  in  previous  pages,  in  cer- 
tain cases  it  does  not  dissolve  all  the  bitumen  which  is  soluble 
in  the  latter  solvent.  On  this  account  it  is  never  used  for  the 
determination  oi  total  bitumen,  but  only  to  discover  the  percent- 
age of  bitumen  which  is  soluble  in  bisulphide  of  carbon,  which  it 
does  not  dissolve,  as  a  means  of  differentiating  the  amount  of 
material  which  has  been  injured  by  natural  weathering  or  over- 
heating, for  which  purpose  it  is  extremely  useful.  The  specific 
gravity  of  the  pure  carbon  tetrachloride  is  1.604  at  15°  C.,  but  the 


SOLVENTS. 


591 


commercial  supply  often  contains  sufficient  bisulphide  of  carbon 
to  lower  this.  Bisulphide  of  carbon  can  be  largely  removed  by 
blowing  a  current  of  air  through  the  solvent  or  by  distilling  it  with 
a  Young  dephlegmator  *  until  the  boiling-point  reaches  76.6°  C. 
The  best  carbon  tetrachloride  found  on  the  market  was  that  fur- 
nished by  the  Acker  Process  Company,  Niagara  Falls,  N.  Y.  This 
had  a  density  of  1.604,  whereas  inferior  supplies  may  fall  as  low 
as  1.593.  This  concern  has,  however,  gone  out  of  business,  and 
the  less  pure  and  more  expensive  German  product  must  now  be 
used  after  redistillation. 

Ethyl  Ether. — No  objection  can  be  raised  to  the  use  of  ether 
for  the  determination  of  malthenes  if  the  purest  product  made  by 
Squibb  is  used.  The  cost  of  this  is,  however,  prohibitive  in  a  labo- 
ratory where  any  large  amount  of  work  is  carried  on.  Commercial 
ether  is  too  impure  and  too  irregular  hi  composition  to  be  used 
for  the  purpose;  it  contains  alcohol  and  water.  The  use  of  ether 
as  a  solvent  must,  therefore,  be  abandoned. 

Acetone. — The  acetone  found  on  the  market  under  the. designa- 
tion "chemically  pure"  is  of  fairly  constant  boiling-point,  that  of 
the  pure  material  being  56.5°  C. 

BOILING-POINT. 


Temperature. 

Per  Cent  Distillate. 

56°  to  57°  C. 
57°  "  58°  C. 
58°  "  59°  C. 
59°  "  60°  C. 
Residue 

26.6% 
58.4 
9.0 
4.0 
2.0 

100.0 

This  solvent  is,  like  ether,  very  expensive,  50  cents  per  pound, 
and  its  general  use  is  prohibited  by  this  fact. 

Commercial  acetone,  costing  $1.75  per  gallon,  is  quite  unsuitable 
for  use  as  a  solvent  owing  to  its  lack  of  purity  and  uniformity.  A 


1  J.  Chem.  Soc.,  1899,  75,  II,  699. 


592 


THE   MODERN   ASPHALT    PAVEMENT. 


specimen  distilled  in  the  author's  laboratory  gave  the  following 
fractions: 

BOILING-POINT. 


Temperature. 

Per  Cent  Distillate. 

56.  8°  to  57°  C. 

2.9% 

57°  to  58°  C. 

13.7 

58°       59°  C. 

32.2 

59°       60°  C. 

15.4 

60°       61°  C. 

9.1 

61°       62°  C. 

4.8 

62°       63°  C. 

4.8 

63°       64°  C. 

2.9 

64°       65°  C. 

2.4 

65°       70°  C. 

4.3 

70°       75°  C. 

3.3 

75°       80°  C. 

2.2 

Residue 

2.0 

100.0 

It  is  evident  that  the  commercial  material  consists  largely 
of  substances  boiling  at  higher  temperature  than  pure  acetone.  It 
will,  for  the  reasons  given,  never  be  used  as  a  standard  solvent. 

Light  Petroleum  Distillates. — Light  petroleum  distillates  have 
been  very  generally  used  for  the  separation  of  the  softer  constitu- 
ents of  the  solid  bitumens,  but  different  analysts  have  used  it  of 
various  boiling-points  and  densities.  None  of  these  solvents  con- 
sists, of  course,  of  any  one  hydrocarbon;  they  are  mixtures  chiefly 
of  isopentane,  pentane,  isohexane,  hexane,  isoheptane,  heptane  and 
the  octanes  in  62°  naphtha,  together  with  small  percentages  of  other 
hydrocarbons  such  as  methylene,  pentamethylene  and  hexamethy- 
lene,  but  the  amounts  of  the  latter  are  too  small  to  have  any  bearing 
upon  the  solvent  power.  The  boiling  points  of  the  principal  con- 
stituents of  the  naphthas  are,  according  to  Young : l 


J.  Chem.  Soc.,  1898,  73,  II,  906. 


SOLVENTS. 
BOILING-POINTS. 


593 


Name. 

760  Milli- 
meters. 

28°  C. 

36°  C. 

Pentainethylene.  .  .  .  .        

50°  C. 

61°  C. 

69°  C. 

M0t  hyl  pentarnet  hy  lene 

72°  C 

Benzene.  .  .             

80°  C. 

81°  C. 

90°  C. 

98°  C. 

Methylhexaniethylene     • 

102°  C. 

Toluene.  . 

111°  C. 

125°  C. 

On  fractioning  a  naphtha  of  88°  Beaume  density  with  a  Young 
dephlegmator  of  eighteen  sections  the  following  results  were  ob- 
tained: 

BOILING-POINT. 


Temperature. 

Per  Cent  of 
Distillate. 

Specific  Gravity 
20°  C/20°  C. 

25°  to  30°  C. 

21.5% 

.6287 

30°       35°  C. 

8.8 

.6324 

35°       40°  C. 

12.7 

.6287 

40°       45°  C. 

13.6 

.6317 

45°       50°  C. 

11.2 

.6448 

50°       55°  C. 

5.6 

.6589 

55°       60°  C. 

4.8 

.6539 

60°       65°  C. 

8.8 

.6566 

65°       70°  C. 

3.2 

.6673 

Residue 

9.8 

.7027 

100.0 

It  is  evident  from  the  above  figures  that  this  naphtha  is  far  from 
being  composed  of  a  single  hydrocarbon.  It  contains  a  preponder- 
ance of  iso-  and  normal  pentanes  and  isohexane,  but  it  would  require 
a  very  large  number  of  fractionations1  with  the  most  perfect  form 


See  Young,  "  Fractional  Distillation,"  Macmillan  &  Co.,  1903. 


594  THE  MODERN   ASPHALT   PAVEMENT. 

of  dephlegmator  to  obtain  a  single  hyrdocarbon  or  even  a  mixture 
of  pentanes.  One  distillation,  with  no  definite  specifications  of  the 
method,  would  have  little  or  no  effect;  and,  in  practice,  it  has  not 
been  found  to  result  in  any  improvement  of  the  naphtha  as  a  sol- 
vent commensurate  with  the  trouble  involved.  The  same  is  the 
case  with  74°  and  62°  Beaume  naphtha.  The  least  dense  of  these 
naphthas  consists  of  a  mixture  of  hydrocarbons,  the  most  prominent 
of  which  are  the  hexanes,  the  more  dense  one  containing  heptanes 
and  octanes.  The  author,  therefore,  considers  it  necessary  to 
merely  see  that  the  density  of  every  lot  of  naphtha  in  use  should  be 
a  standard  one,  such  as  .7290  for  62°  Beaume,  .6863  for  74°  Beaume, 
and  .6422  for  88°  Beaume".  If  the  lot  in  hand  is  denser  than  the 
standard  it  must  be  rejected,  but  if  it  is  lighter  it  can  be  brought 
to  the  standard,  in  the  case  of  the  88°  Beaume  solvent,  by  blowing 
with  a  current  of  air  for  a  short  time,  or  in  the  heavier  ones  by 
distillation.  The  solvent  power  in  this  way  will  be  found  to  be 
quite  as  uniform  among  different  lots  as  if  a  single  fractionation 
was  attempted. 

It  remains  to  determine  whether  there  is  a  preference  for  one 
density  of  naphtha  over  another.  If  one  alone  is  to  be  used  that 
of  74°  Beaume  may  be  well  accepted  as  being  a  solvent  of  medium 
power,  but  the  author  has  found  that  the  use  of  both  88°  and  62° 
Beaume  naphtha  is  most  desirable,  as  in  this  way  a  more  thorough 
differentiation  can  be  accomplished.1 

From  the  preceding  data  it  would  seem  that  the  desirable 
solvents  for  use  in  the  asphalt-paving  industry  are  those  which 
have  been  mentioned  in  the  chapter  on  Methods  of  Analysis; 
bisulphide  of  carbon  for  the  total  bitumen,  carbon  tetrachloride  for 
the  detection  of  bitumen  which  has  been  affected  by  overheating  or 
weathering,  and  88°  and  62°  Beaume  naphtha  for  the  purpose  of 
determining  whether  a  bitumen  shows  a  normal  relation  between 
the  amounts  dissolved  by  these  two  solvents  or  points  to  the  addi- 
tion of  a  flux  to  an  extremely  hard  asphalt. 

1  See  page  542. 


CHAPTER   XXX. 

EQUIPMENT  OF  A  LABORATORY  FOR  CONTROL  OF 
ASPHALT   WORK. 

FOR  making  the  necessary  determinations  for  the  control  of 
the  materials  and  mixtures  in  use  in  the  construction  of  an  asphalt 
pavement,  according  to  the  methods  which  have  been  outlined  in 
a  previous  chapter,  no  elaborate  laboratory  is  necessary.  Sub- 
laboratories  for  this  purpose  have  been  established  economically  by 
the  author  at  many  plants  under  his  control. 

The  room  which  is  to  be  used  need  not  be  large,  but  should  be 
well  lighted.  It  should  contain  several  tables  securely  fastened 
to  the  wall.  That  upon  which  the  balance  and  penetration 
machine  are  to  be  placed  should  be  as  free  from  vibration  as 
possible. 

The  equipment  usually  supplied  for  such  a  laboratory  consists 
of  the  following  pieces  of  apparatus: 

1  Chaslyn  balance $15  00 

2  Bunsen  burners,   No.   2597,  Eimer  &   Amend, 

New  York 2  00 

1  Fairbanks  sand  scale,  No.  485,  Fairbanks  Co., 

New  York 6  00 

1  set  of  sieves  (200,  100,  80,  50,  40,  30,  20,  10 

mesh) , 15  75 

1  New  Y'ork  Testing  Laboratory  Penetrometer, 

Howard  &  Morse,  1197  DeKalb  Avenue,  Brook- 
lyn, N.  Y 60  00 

2  thermometers  for  penetrometer,  C.  J.  Tagliabue 

Co.,  N.  Y 2  50 

595 


596  THE  MODERN    ASPHALT    PAVEMENT. 

1  doz.  2i"  glass  funnels,  E.  &  A.  No.  3345 1  20 

1  doz.  watch  glasses  to  cover  funnels,  E.  &  A.  No. 

7189 56 

1  doz.  Erlenmeyer  flasks,  Jena  glass,  200  cc.,  E. 

&  A.  No.  3863 1  68 

}  doz.  4J"  porcelain  evaporating  dishes,  E.  &  A. 

No.  2963 2  70 

}  doz.  watch  glasses  to  cover  dishes,  E.  &  A.  No. 

7189 75 

J  doz.  Royal  Berlin  porcelain  crucibles,  No.  0,  with- 
out covers,  E.  &  A.  No.  2850 1  38 

4  Royal  Berlin  porcelain  crucibles  No.  2, 

without  covers,  E.  &  A.  No.  2850 1  40 

4  packages  filter  paper,  S.  &  S.  No.  597,  E.  &  A. 

No.  3213  (3i'r) 1  00 

1  glass  cylinder,  graduated  to  100  cc.,  E.  &  A.  No. 

2919 70 

J  doz.  flat  bottom  sample  tubes,  4"  high  by  f " 

diameter,  E.  &  A.  No.  4647 30 

1  pair  tongs,  E.  &  A.  No.  2883-B 85 

2  iron  ring  stands,  E.  &  A.  No.  4812 1  30 

2  iron  sand  baths,  6"  deep  form,  E.  &  A.  No.  4555  44 

1  spatula,  4",  E.  &  A.  No.  4643 25 

1  spatula,  6",  E.  &  A,  No.  4643 35 

1  spatula,  8",  E.  &  A.  No.  4643 55 

3  clay  triangles,  small,  to  fit  R.  B.  crucibles,  No. 

0,  E.  &  A.  No.  4965 25 

3  clay  triangles,  large,  to  support  porcelain 

evaporating  dishes,  E.  &  A.  No.  4965 25 

1  brass  mold  for  flow  test 1 1  25 

3  brass  flow  plates 1 1  65 

1  New  York  Testing  JLaboratory-Seebach  drying 

oven  (Hauck-Seebach  Co.,  291  Essex  Street, 

Brooklyn,  New  York.) 25  00 

1  doz.  crystallizing  dishes,  straight  sides,  2\" 

diameter,  E.  &  A.  No.  2960 1  68 

1  New  York  Testing  Laboratory,  Maurer,  N.  J. 


EQUIPMENT    OF    A    LABORATORY.  597 

2  chemical  thermometers,  50-600°  F.,  gas  filled, 

style  No.  4881 $5  00 

J  doz.  camel's  hair  brushes,  large  size,  E.  &  A.  No. 

2943 , 18 

1  New  York  State  Board  of  Health  oil  tester  with 

Bunsen  burner,  E.  &  A.  No.  4160 8  00 

J  doz.  beakers,  600  cc.,  115  mm.  high  and  85  mm. 

diameter,  E.  &  A.  No.  3872 1  80 

1  foot  blower,  small,  E.  &  A.  No.  2308 4  00 

J  pound  glass  tubing,  TV'  diameter 15 

J  "  glass  rod,  J"  diameter 15 

1  washing  bottle,  1  quart,  E.  &  A.  No.  7181 75 

50  pounds  carbon  disulphide,  at  10  cents 5  00 

5  gallons  88°  naphtha,  at  20  cents 1  00 

1  piece  rubber  tubing,  Ty,  E.  &  A.  No.  4540 2  00 

1  gross  2-oz.  flat  tin  boxes,  E.  &  A.  No.  2482 1  38 


$176  15 

The  prices  given  are  list,  and  an  estimate  should  be  requested 
before  placing  an  order,  as  discounts  are  given. 

The  use  of  the  above  apparatus  has  been  described  in 
the  methods.  The  Primus  burner  is  the  most  convenient 
one  at  points  where  gas  is  not  available,  as  it  burns  kerosene 
and  is  kept  clean  more  easily  than  the  Barthel  burner,  which  burns 
benzine,  62°  Beaume  naphtha. 

With  the  preceding  outfit  in  the  hands  of  a  clever  yard-foreman 
or  assistant  a  contractor  or  a  city  official  should  be  able,  following 
the  methods  which  have  been  described,  to  control  accurately  the 
work  under  his  direction. 


APPENDIX. 


As  a  type  of  modern  asphalt  paving  specifications,  those  of 
Kansas  City,  Mo.,  for  1907,  are  appended  for  the  information  of 
the  reader.  As  this  book  goes  to  press  modified  specifications  are 
in  course  of  preparation  in  Kansas  City,  Mo. 

BINDER  COURSE. 

Upon  the  base  of  cement  concrete  there  shall  be  laid  a  binder  course 
of  asphaltic  concrete  which,  when  ultimately  compressed  by  rolling,  shall 
have  an  average  thickness  of ( )  inches,  and  shall  be  com- 
posed and  laid  as  follows:  The  Binder  Course  shall  consist  principally  of 
clean  broken  stone,  which  shall  pass  through  a  one  (1)  inch  screen.  To  this 
stone  shall  be  added  well  graded  sand,  or  reduced  old  asphaltic  surface 
mixture  (which  consists  principally  of  sand)  in  a  sufficient  quantity  to  fill 
the  voids  between  the  stone  when  laid  in  mass.  The  old  Asphaltic  Surface 
mixture  used  in  the  binder  course  before  being  used  shall  be  reduced  by 
being  thoroughly  disintegrated.  To  the  materials  just  described  shall  be 
added  a  sufficient  quantity  of  asphaltic  cement  to  thoroughly  coat  each 
particle  of  the  composition. 

The  Asphaltic  Cement  to  be  used  in  the  Binder  Course  shall  be  composed 
of  a  refined  asphalt  fluxed  with  a  heavy  petroleum  oil  or  liquid  asphalt. 
This  asphaltic  cement  shall  be  composed  of  such  materials  as  will  fulfill  the 
chemical  and  physical  tests  required  of  the  asphaltic  cement  for  the  Asphalt 
Wearing  Surface. 

These  component  materials  shall  be  combined  and  mixed  while  hot  by 
machinery  in  such  proportions  that  the  percentage  of  bitumen  in  the  binder 
when  laid  shall  approximately  be  from  3  per  cent  to  6  per  cent  by  weight 
of  the  total  mixture,  and  such  that  the  aggregate  mass  shall,  when  laid  and 
rolled,  form  a  dense  compact  asphaltic  concrete  suitable  and  capable  of 
sustaining  an  asphalt  wearing  surface  without  vibration.  The  mixture 
thus  prepared  shall  be  spread  upon  the  street  base  with  rakes  while  in  a  hot 
plastic  condition,  and  shall  be  rammed  and  rolled  until  it  forms  a  compact 

599 


600  THE   MODERN  ASPHALT  PAVEMENT. 

and  thoroughly  bonded  binder  course  of  the  required  thickness,  and  its  top 
surface  shall  be  approximately  parallel  with  the  completed  surface  of  the 
pavement. 

The  binder  course  shall  not  be  laid  upon  the  concrete  base  until  the 
expiration  of  at  least  ten  (10)  days  in  case  Natural  Cement  Concrete  is 
used,  or  until  the  expiration  of  at  least  five  (5)  days  in  case  Portland  Cement 
Concrete  is  used,  and  then  only  when  the  Engineer  is  satisfied  that  the  con- 
crete has  set  sufficiently  hard  to  bear  the  weight  of  a  ten  ton  roller. 
HI  The  surface  of  the  concrete  foundation  shall  be  swept  clean  and  shall 
be  dry  during  the  laying  of  the  binder,  which  shall  not  come  in  contact  with 
moist  or  frozen  surfaces.  No  traffic  on  the  binder  of  horses  or  vehicles  is 
to  take  place  except  such  as  is  required  to  lay  the  asphalt  pavement  surface 
layer  thereon.  The  traffic  then  necessary  shall  in  no  way  injure  the  Binder. 
The  surface  of  the  Binder  must  be  kept  clean  at  all  times  and  in  perfect 
condition,  so  as  to  facilitate  the  adhesion  of  the  asphalt  pavement  when 
laid  upon  it. 

ASPHALT  WEARING  SURFACE. 

The  wearing  surface  shall  be  laid  upon  the  binder  course  and,  when 

thoroughly  compressed,  shall  have  an  average  thickness  of ( ) 

inches.  The  wearing  surface  shall  consist  of  a  uniform  mixture  of  asphaltic 
cement,  sand  and  a  mineral  filler,  but  the  asphaltic  cement  and  mineral 
filler  may  be  used  without  separation  and  in  their  natural  state  of  com- 
bination or  mixture. 

The  asphaltic  cement,  when  considered  apart  from  the  mineral  matter, 
shall  have  the  following  characteristics: 

It  shall  be  free  from  water  or  decomposition  products. 

The  various  hydrocarbons  composing  it  shall  be  present  in  homogeneous 
solution,  no  oily  or  granular  character  being  present. 

PENETRATION. — It  must,  when  tested  at  77  deg.  Fahrenheit,  have  a 
penetration  of  from  3  to  9  millimeters  when  tested  for  five  seconds  with  a 
No.  2  needle  weighted  with  100  grams,  according  to  the  nature  of  the  asphalt 
and  the  conditions  under  which  it  is  employed.  It  must  not  be  so  suscep- 
tible to  changes  of  temperature  that  if  at  32  deg.  Fahrenheit  it  shows  a  hard- 
ness indicated  by  1  millimeter  penetration,  at  115  deg.  Fahrenheit  it  will 
not  be  so  soft  as  to  give  more  than  35  millimeters  penetration,  using  the 
above  method  of  testing. 

Twenty  (20)  grams  of  it  shall  not  lose  more  than  four  (4)  per  cent  in 
weight  upon  being  maintained  at  a  uniform  temperature  of  325  deg.  Fahr- 
enheit for  seven  (7)  hours  in  a  cylindrical  vessel  two  and  one-half  (2£) 
inches  hi  diameter  by  two  (2)  inches  high. 

Twenty  (20)  grams  of  it  shall  not  lose  more  than  eight  and  one-half  (8£) 
per  cent  upon  being  maintained  at  a  uniform  temperature  of  400  deg. 


APPENDIX  601 

• 

Fahrenheit  for  seven  (7)  hours  in  a  cylindrical  vessel  two  and  one-half  (2$) 
inches  in  diameter  by  two  (2)  inches  high. 

It  shall  be  soluble  in  chemically  pure  carbon  disulphide  at  air  tempera- 
ture to  the  extent  of  at  least  ninety-five  (95)  per  cent. 

It  shall  not  contain  of  carbonaceous  matter  insoluble  in  chemically  pure 
carbon  disulphide,  air  temperature,  more  than  four  and  one-half  (4£)  per 
cent. 

It  shall  be  soluble  in  87  deg.  Beaume*  petroleum  naphtha,  air  temperature, 
to  the  extent  of  not  less  than  sixty-five  (65)  per  cent  and  not  more  than 
eighty  (80)  per  cent. 

Its  solubility  in  carbon  tetrachloride  shall  not  be  more  than  one  and 
one-half  (H)  per  cent  less  than  its  solubility  in  carbon  disulphide — both 
tests  being  made  at  air  temperature. 

It  shall  show  of  fixed  carbon  not  more  than  fifteen  (15)  per  cent. 

It  shall  show  a  flashing  point  (New  York  State  Closed  Oil  Tester)  of 
more  than  350  deg.  Fahrenheit. 

It  shall  not  contain  more  than  three  (3)  per  cent  of  paraffine  scale,  the 
Holde  method  of  determining  paraffine  scale  being  used. 

USE. — The  bitumen  entering  into  the  composition  shall  have  been  in 
use  in  the  street  paving  industry  under  conditions  similar  to  those  con- 
templated in  this  contract,  at  least  four  (4)  years  prior  to  the  letting  of  this 
contract.  The  asphaltic  cement  shall  constitute  not  less  than  nine  and 
one-half  (9£),  nor  more  than  thirteen  (13)  per  cent  of  the  surface  mixture. 

MIXING. — While  the  ingredients  of  the  asphalt  wearing  surface  are  being 

mixed,  and  at  the  time  it  is  being  taken  from  the  mixer  for  use,  the  paving 

I  composition  must  be  thoroughly  agitated  at  a  temperature  of  between 

275  deg.  and  330  deg.  Fahrenheit,  and  if  any  part  of  it  settles,  it  must  be 

again  thoroughly  agitated  before  being  used. 

The  characteristics  of  this  material  and  the  tests  herein  required  to  be 
complied  with  are  to  be  met  at  the  time  of  making  and  laying  the  pave- 
ment. It  is  recognized  that  its  properties  change  somewhat  upon  being 
exposed  to  weather  and  street  traffic. 

The  asphaltic  cement  used  under  this  contract  must  not  be  materially 
changed  as  to  the  brands,  kinds,  proportions  and  qualities  of  the  ingredients 
of  the  mixture  during  the  progress  of  the  work. 

The  materials,  the  machinery,  testing  apparatus  and  the  works  of  the 
Contractor  shall  at  all  times  between  the  date  of  the  contract  for  the  work 
and  the  completion  of  the  work,  be  open  to  inspection  of  the  City  Engineer 
for  the  purpose  of  enabling  him  to  determine  whether  the  requirements  of 
these  specifications  are  being  complied  with.  No  asphaltic  cement  injured 
by  heating,  or  otherwise,  will  be  permitted  to  go  into  the  work. 

SAND. — The  sand  must  be  clean  and  sharp  and  shall  not  be  of  uniform 
size,  but  various  percentages  shall  pass  sieves  of  the  following  square  mesh 
per  linear  inch:  200,  100,  80,  50,  40,  30,  20,  and  10. 


602  THE   MODERN    ASPHALT   PAVEMENT. 

It  shall  be  present  in  the  surface  mixture  to  such  an  extent  that  not  less 
than  three  (3)  per  cent  nor  more  than  eight  (8)  per  cent  of  such  surface 
mixture  shall  consist  of  sand  passing  a  200  mesh  sieve;  that  not  less  than 
fifteen  (15)  per  cent  nor  more  than  thirty-two  (32)  per  cent  shall  pass  an 
80  and  be  retained  by  a  200  mesh  sieve ;  that  not  less  than  twenty-five  (25) 
per  cent  nor  more  than  forty-five  (45)  per  cent  shall  pass  a  40  and  be 
retained  by  an  80  mesh  sieve;  that  not  less  than  ten  (10)  per  cent  nor 
more  than  thirty  (30)  per  cent  shall  pass  a  10  and  be  retained  by  a  40  mesh 
sieve. 

The  mineral  particles,  including  limestone  or  Portland  cement,  which 
when  thoroughly  mixed  by  air  blast,  or  otherwise,  with  distilled  water  at  a 
temperature  of  77  deg.  Fahrenheit,  will  subside  in  fifteen  (15)  seconds,  is 
by  the  terms  of  this  contract  regarded  as  sand.  This  test  shall  be  conducted 
in  a  beaker  about  six  (6)  inches  high  and  nearly  full  of  the  water  and  mate- 
rial to  be  tested. 

FILLER. — The  filler  shall  be  composed  of  mineral  particles  so  small  that 
when  they  are  thoroughly  agitated  with  distilled  water  at  a  temperature 
of  77  deg.  Fahrenheit,  by  means  of  an  air  blast,  or  otherwise,  they  will  not 
subside  in  fifteen  (15)  seconds,  but  can  be  poured  off  with  the  water  after  a 
lapse  of  fifteen  (15)  seconds  from  the  time  agitation  ceased.  This  test  is  to 
be  carried  out  in  a  beaker  as  described  in  the  preceding  paragraph.  Such 
fine  mineral  matter  shall  be  insoluble  in  water  and  shall  by  the  terms  of 
this  contract  be  known  as  filler  and  shall  constitute  not  less  than  four  (4) 
per  cent  nor  more  than  seven  (7)  per  cent  of  the  total  wearing  surface. 

The  exact  proportions  of  all  constituents  of  the  wearing  surface  to  be 
determined  by  the  Contractor  shall  be  subject  to  the  approval  of  the  City 
Engineer. 

The  sand  and  asphaltic  cement  shall  be  heated  separately  to  about  330 
deg.  Fahrenheit.  The  mineral  filler  will  be  mixed  while  cold  with  the  sand 
while  hot,  and  which  shall  have  been  heated  to  about  330  deg.  Fahrenheit, 
and  then  this  composition  shall  be  mixed  with  the  asphaltic  cement  at  the 
temperature  stated,  in  such  a  manner  and  with  such  apparatus  as  to  effect 
a  thoroughly  homogeneous  mixture. 

Samples  of  all  material  entering  into  the  composition  of  the  pavement 
shall  be  supplied  to  the  City  Engineer,  when  required,  in  suitable  tin  boxes 
and  cans,  and  the  Contractor,  when  required,  shall  give  to  the  Engineer  a 
written  statement  of  the  date  and  geographical  source  of  all  crude  or  other 
materials  from  which  the  refined  asphaltum  is  made,  and  proportions  of 
each,  also  per  cent  of  pure  bitumen  contained  therein.  The  City  Engineer, 
or  his  representatives,  shall  have  access  to  all  branches  of  the  works  at  any 
time.  He,  or  his  representatives,  shall  inspect  the  material  mrnished  and 
work  done  upon  the  asphalt  pavement,  and  have  power  to  enforce  all  require- 
ments of  specifications.  He  shall  at  all  times  have  access  to  the  works  and 
laboratories  of  the  Contractors,  and  shall  have  privilege  to  take  samples 


APPENDIX.  603 

from  such  works,  or  from  material  upon  the  streets,  as  may  be  deemed 
advisable  or  necessary  for  testing  purposes. 

It  shall  be  the  duty  of  the  Contractor,  when  performing  work  under  the 
contract,  to  furnish  complete  detailed  analyses  of  the  ingredients  of  the 
paving  mixture  to  the  City  Engineer,  whenever  requested  by  him  so  to  do. 

The  paving  mixture  prepared  in  the  manner  thus  indicated  shall  be 
brought  to  the  ground  in  carts  or  wagons  at  a  temperature  of  not  less  than 
250  deg.  nor  more  than  350  deg.  Fahrenheit.  If  the  temperature  of  the 
air  is  less  than  60  deg.  Fahrenheit,  the  Contractor  must  provide  canvas 
covers  for  use  in  transit.  It  will  then  be  thoroughly  spread  by  means  of 
hot  rakes  in  such  a  manner  as  to  give  a  uniform  and  regular  grade,  so  that 
after  having  reached  its  ultimate  compression  it  shall  have  a  thickness  shown 
on  the  plans  and  required  in  the  specifications.  This  depth  shall  be  con- 
stantly tested  by  means  of  gauges.  The  surface  shall  then  be  compressed 
by  a  small  steam-roller  or  hand-roller,  after  which  a  small  amount  of 
Hydraulic  Cement  will  be  spread  over  it,  and  it  will  then  be  thoroughly 
compressed  by  a  steam-roller  weighing  not  less  than  two  hundred  and  fifty 
(250)  pounds  to  the  inch  run,  the  rolling  being  continued  for  not  less  than 
five  (5)  hours  for  every  thousand  square  yards  of  surface. 

ASPHALTIC  WEARING  SURFACE. — The  acceptance  of  said  work  by  the 
City  Engineer  after  its  completion,  shall  be  conclusive  of  the  fact  that  the 
provisions  hereof  under  the  above  heading,  "Asphalt  Wearing  Surface," 
has  been  complied  with. 

REPAIRS. — All  repairs  of  asphalt  pavement  required  to  be  made  by  the 
Contractor  during  the  guarantee  period  shall  be  made  with  mixtures  similar 
and  equal  to  and  laid  in  the  manner  of  those  described  above. 


604 


THE    MODERN    ASPHALT    PAVEMENT. 


COMPARISON  OF  ACTUAL  SPECIFIC  GRAVITY  AND  DEGREES 
BEAUM£  HYDROMETER. 

140 
For  liquids  lighter  than  water,  specific  gravity  =  at  60°  F. 


0  E4. 

Sp.  Gr. 

°Bd. 

Sp.  Gr. 

°B£. 

Sp.  Gr. 

0  B<*. 

Sp.  Gr. 

10.0 

1.0000 

14.0 

0.9722 

18.0 

0.9459 

22.0 

0.9211 

.1 

0.9993 

.1 

0.9715 

.1 

0.9453 

.1 

0.9204 

.2 

0.9986 

.2 

0.9709 

.2 

0.9447 

.2 

0.9198 

.3 

0.9979 

.3 

0.9702 

.3 

0.9440 

.3 

0.9192 

.4 

0.9972 

.4 

0.9695 

.4 

0.9434 

.4 

0.9186 

.5 

0.9964 

.5 

0.9689 

.5 

0.9428 

.5 

0.9180 

.6 

0.8957 

.6 

0.9682 

.6 

0.9421 

.6 

0.9174 

.7 

0.9950 

.7 

0.9675 

.7 

0.9415 

.7 

0.9168 

.8 

0.9943 

.8 

0.9669 

.8 

0.9409 

.8 

0.9162 

.9 

0.9936 

.9 

0.9662 

.9 

0.9402 

.9 

0.9156 

11.0 

0.9929 

15.0 

0.9655 

19.0 

0.9396 

23.0 

0.9150 

.1 

0.9922 

.1 

0.9649 

.1   0.9390 

.1 

0.9144 

.2 

0.9915 

.2 

0.9642 

.2  i  0.9383 

.2 

0.9138 

.3 

0.9908 

.3 

0.9635 

.3   0.9377 

.3 

0.9132 

.4 

0.9901 

.4 

0.9629 

.4   0.9371 

.4 

0.9126 

.5 

0.9894 

.5 

0.9622 

.5   0.9365 

.5 

0.9121 

.6 

0.9887 

.6 

0.9615 

.6 

0.9358 

.6 

0.9115 

.7 

0.9880 

.7 

0.9609 

.7 

0.9352 

.7 

0.9109 

.8 

0.9873 

.8 

0.9602 

.8   0.9346 

.8 

0.9103 

.9 

0.9866 

.9 

0.9596 

.9   0.9340 

.9 

0.9097 

12.0 

0.9859 

16.0 

0.9589 

20.0   0.9333 

24.0 

0.9091 

.1 

0.9852 

.1 

0.9582 

.1   0.9327 

.1 

0.9085 

.2 

0.9845 

2 

0.9576 

.2   0.9321 

.2 

0.9079 

.3 

0.9838 

.3 

0.9569 

.3 

0.9315 

.3 

0.9073 

.4 

0.9831 

.4 

0.9563 

.4 

0.9309 

.4 

0.9067 

.5 

0.9825 

.5 

0.9556 

.5   0.9302 

.5 

0.9061 

.6 

0.9818 

.6 

0.9550 

.6  !  0.9296 

.6 

0.9056 

•7 

0.9811 

.7 

0.9543 

.7  i  0.9290 

.7 

0.9050 

'.& 

0.9804 

.8 

0.9537 

Q 

0.9284 

.8 

0.9044 

.9 

0.9797 

.9 

0.9530 

'.9 

0.9278 

.9 

0.9038 

13.0 

0.9790 

17.0 

0.9524 

21.0 

0.9272 

36.0 

0.9032 

.1 

0.9783 

.1 

0.9517 

.1 

0.9265 

.1 

0.9026 

.2 

0.9777 

.2 

0.9511 

.2 

0.9259 

.2 

0.9021 

.3 

0.9770 

.3 

0.9504 

.3 

0.9253 

.3 

0.9015 

.4 

0.9763 

.4 

0.9498 

.4 

0.9247 

.4 

0.9009 

.5 

0.9756 

.5 

0.9492 

.5 

0.9241 

,5 

0.9003 

.6 

0.9749 

.6 

0.9485 

.6 

0.9235 

.6 

0.8997 

.7 

0.9743 

.7 

0.9479 

.7 

0.9229 

.7 

0.8992 

.8 

0.9736 

.8 

0.9472 

.8 

0.9223 

.8 

0.8986 

.9 

0.9729 

.9 

0.9466 

.9 

0.9217 

.9 

0.8980 

I 

APPENDIX. 


605 


COMPARISON   OF  ACTUAL   SPECIFIC   GRAVITY  AND   DEGREES 
BEAUM6  HYDROMETER— Continued. 


°B£ 

Sp.  Gr. 

°B<5. 

Sp.  Gr. 

°B<?. 

Sp.  Gr. 

°B«$. 

Sp.  Gr. 

26.0 

0.8974 

31.0 

0.8696 

36.0 

0.8434 

41.0 

0.8187 

.1 

0.8969 

.1 

0.8690 

.1 

0.8429 

.1 

0.8182 

.2 

0.8963 

.2 

0.8685 

.2 

0.8424 

.2 

0.8178 

.3 

0.8957 

.3 

0.8679 

.3 

0.8419 

.3 

0.8173 

.4 

0.8951 

.4 

0.8674 

.4 

0.8413 

.4 

0.8168 

.5 

0.8946 

.5 

0.8669 

.5 

0.8408 

.5 

0.8163 

.6 

0.8940 

.6 

0.8663 

.6 

0.8403 

.6 

0.8159 

.7 

0.8934 

.7 

0.8658 

.7 

0.8398 

.7 

0.8154 

.8 

0.8929 

.8 

0.8653 

.8 

0.8393 

.8 

0.8149 

.9 

0.8923 

.9 

0.8647 

.9 

0.8388 

.9 

0.8144 

27.0 

0.8917 

32.0 

0.8642 

37.0 

0.8383 

42.0 

0.8140 

.1 

0.8912 

.1 

0.8637 

.1 

0.8378 

.1 

0.8135 

.2 

0.8906 

.2 

0.8631 

.2 

0.8373 

.2 

0.8130 

.3 

0.8900 

.3 

0.8626 

.3 

0.8368 

.3 

0.8125 

.4 

0.8895 

.4 

0.8621 

.4 

0.8363 

.4 

0.8121 

.5 

0.8889 

.5 

0.8615 

.5 

0.8358 

.5 

0.8116 

.6 

0.8883 

.6 

0.8610 

.6 

0.8353 

.6 

0.8111 

.7 

0.8878 

.7 

0.8605 

.7 

0.8348 

.7 

0.8107 

.8 

0.8872 

.8 

0.8600 

.8 

0.8343 

.8 

0.8102 

.9 

0.8866 

.9 

0.8594 

.9 

0.8338 

.9 

0.8097 

28.0 

0.8861 

33.0 

0.8589 

38.0 

0.8333 

43.0 

0.8092 

.1 

0.8855 

.1 

0.8584 

.1 

0.8328 

.1 

0.8088 

.2 

0.8850 

.2 

0.8578 

.2 

0.8323 

.2 

0.8083 

.3 

0.8844 

.3 

0.8573 

.3 

0.8318 

.3 

0.8078 

.4 

0.8838 

.4 

0.8568 

.4 

0.8314 

.4 

0.8074 

.5 

0.8833 

.5 

0.8563 

.5 

0.8309 

.5 

0.8069 

.6 

0.8827 

.6 

0.8557 

.6 

0.8304 

.6 

0.8065 

.7 

0.8822 

.7 

0.8552 

.7 

0.8299 

.7 

0.8060 

.8 

0.8816 

.8 

0.8547 

.8 

0.8294 

.8 

0.8055 

.9 

0.8811 

.9 

0.8542 

.9 

0.8289 

.9 

0.8051 

29.0 

0.8805 

34.0 

0.8537 

39.0 

0.8284 

44.0 

0.8046 

.1 

0.8799 

.1 

0.8531 

.1 

0.8279 

.1 

0.8041 

.2 

0.8794 

.2 

0.8526 

.2 

0.8274 

.2 

0.8037 

.3 

0.8788 

.3 

0.8521 

.3 

0.8269 

.3 

0.8032 

.4 

0.8783 

.4 

0.8516 

.4 

0.8264 

.4 

0.8028 

.5 

0.8777 

.5 

0.8511 

.5 

0.8260 

.5 

0.8023 

.6 

0.8772 

.6 

0.8505 

.6 

0.8255 

.6 

0.8018 

.7 

0.8766 

.7 

0.8500 

.7 

0.8250 

.7 

0.8014 

.8 

0.8761 

.8 

0.8495 

.8 

0.8245 

.8 

0.8009 

.9 

0.8755 

.9 

0.8490 

.9 

0.8240 

.9 

0.8005 

30.0 

0.8750 

35.0 

0.8485 

40.0 

0.8235 

45.0 

0.8000 

.1 

0.8745 

.1 

0.8480 

.1 

0.8230 

.1 

0.7995 

.2 

0.8739 

.2 

0.8475 

.2 

0.8226 

.2 

0.7991 

.3 

0.8734 

.3 

0.8469 

.3 

0.8221 

.3 

0.7986 

.4 

0.8728 

.4 

0.8464 

.4 

0.8216 

.4 

0.7982 

.5 

0.8723 

.5 

0.8459 

.5 

0.8211 

.5 

0.7977 

.6 

0.8717 

.6 

0.8454 

.6 

0.8206 

.6 

0.7973 

.7 

0.8712 

.7 

0.8449 

.7 

0.8202 

.7 

0.7968 

.8 

0.8706 

.8 

0.8444 

.8 

0.8197 

.8 

0.7964 

.9 

0.8701 

.9 

0.8439 

.9 

0.8192 

.9 

0.7959 

606 


THE   MODERN    ASPHALT    PAVEMENT. 


COMPARISON  OF  ACTUAL  SPECIFIC  GRAVITY  AND  DEGREES 
BEAUME  HYDROMETER— Continued. 


°B<5. 

Sp.  Gr. 

0  E4. 

Sp.  Gr. 

0  B6. 

Sp.  Gr. 

°B<;. 

Sp.  Gr. 

46.0 

0.7955 

51.0 

0.7735 

56.0 

0.7527 

61.0 

0.7330 

.1 

0.7950 

.1 

0.7731 

.1 

0.7523 

.1 

0.7326 

.2 

0.7946 

.2 

0.7726 

.2 

0.7519 

.2 

0.7322 

.3 

0.7941 

.3 

0.7722 

.3 

0.7515 

.3 

0.7318 

.4 

0.7937 

.4 

0.7718 

.4 

0.7511 

.4 

0.7315 

.5 

0.7932 

.5 

0.7713 

.5 

0.7507 

.5 

0.7311 

.6 

0.7928 

.6 

0.7709 

.6 

0.7503 

.6 

0?7307 

.7 

0.7923 

.7 

0.7705 

.7 

0.7499 

.7 

0.7303 

.8 

0.7919 

.8 

0.7701 

.8 

0.7495 

.8 

0.7299 

.9 

0.7914 

.9 

0.7697 

.9 

0.7491 

.9 

0.7295 

47.0 

0.7910 

52.0 

0.7692 

57.0 

0.7487 

62.0 

0.7292 

.1 

0.7905 

.1 

0.7688 

.1 

0.7483 

.1 

0.7288 

.2 

0.7901 

.2 

0.7684 

.2 

0.7479 

.2 

0.7284 

.3 

0.7896 

.3 

0.7680 

.3 

0.7475 

.3 

0.7280 

.4 

0.7892 

.4 

0.7675 

.4 

0.7471  . 

.4 

0.7277 

.5 

0.7887 

.5 

0.7671 

.5 

0.7467 

.5 

0.7273 

.6 

0.7883 

.6 

0.7667 

.6 

0.7463 

.6 

0.7269 

.7 

0.7878 

.7 

0.7663 

.7 

0.7459 

.7 

0.7265 

.8 

0.7874 

.8 

0.7659 

.8 

0.7455 

.8 

0.7261 

.9 

0.7370 

.9 

0.7654 

.9 

0.7451 

.9 

0.7258 

48.0 

0.7865 

53.0 

0.7650 

58.0 

0.7447 

63.0 

0.7254 

.1 

0.7861 

.1 

0.7646 

.1 

0.7443 

.1 

0.7250 

.2 

0.7856 

.2 

0.7642 

.2 

0.7439 

.2 

0.7246 

.3 

0.7852 

.3 

0.7638 

.3 

0.7435 

.3 

0.7243 

.4 

0.7848 

.4 

0.7634 

.4 

0.7431 

.4 

0.7239 

.5 

0.7843 

.5 

0.7629 

.5 

0.7427 

.5 

0.7235 

.6 

0.7839 

.6 

0.7625 

.6 

0.7423 

.6 

0.7231 

.7 

0.7834 

.7 

0.7621 

.7 

0.7419 

.7 

0.7228 

.8 

0.7830 

.8 

0.7617 

.8 

0.7415 

.8 

0.7224 

.9 

0.7826 

.9 

0.7613 

.9 

0.7411 

.9 

0.7220 

49.0 

0.7821 

54.0 

0.7609 

59.0 

0.7407 

64.0 

0.7216 

.1 

0.7817 

.1 

0.7605 

.1 

0.7403 

.1 

0.7213 

.2 

0.7812 

.2 

0.7600 

.2 

6.7400 

.2 

0.7209 

.3 

0.7808 

.3 

0.7596 

.3 

0.7396 

.3 

0.7205 

.4 

0.7804 

.4 

0.7592 

.4 

0.7392 

.4 

0.7202 

.5 

0.7799 

.5 

0.7588 

.5 

0.7388 

.5 

0.7198 

.6 

0.7795 

.6 

0.7584 

.6 

0.7384 

.6 

0.7194 

.7 

0.7791 

.7 

0.7580 

.7 

0.7380 

.7 

0.7191 

.8 

0.7786 

.8 

0.7576 

.8 

0.7376 

.8 

0.7187 

.9 

0.7782 

.9 

0.7572 

.9 

0.7372 

.9 

0.7183 

50.0 

0.7778 

55.0 

0.7568 

60.0 

0  .7368 

65.0 

0.7179 

.1 

0.7773 

.1 

0.7563 

.1 

0.7365 

.1 

0.7176 

.2 

0.7769 

.2 

0.7559 

.2 

0.7361 

.2 

0.7172 

.3 

0.7765 

.3 

0.7555 

.3 

0.7357 

.3 

0.7168 

.4 

0.7761 

.4 

0.7551 

.4 

0.7353 

.4 

0.7165 

.5 

0.7756 

.5 

0.7547 

.5 

0.7349 

.5 

0.7161 

.6 

0.7752 

.6 

0.7543 

.6 

0.7345 

.6 

0.7157 

.7 

0.7748 

.7 

0.7539 

.7 

0.7°41 

.7 

0.7154 

.8 

0.7743 

.8 

0.7535 

.8 

0.7338 

.8 

0.7150 

.9 

0.7739 

.9 

0.7531 

.9 

0.7334 

.9 

0.7147 

APPENDIX. 


607 


COMPARISON  OF  ACTUAL  SPECIFIC  GRAVITY  AND  DEGREES 

BEAUM£  HYDROMETER— Continued. 


•B<§. 

Sp.  Gr. 

°B<5.  !   Sp.  Gr. 

°B<*. 

Sp.  Gr. 

°B<«. 

Sp.  Gr. 

66.0 

0.7143 

70.0 

0.7000 

74.0 

0.6863 

78.0 

0.6731 

.1 

0.7139 

.1 

0.6997 

.1 

0.6859 

.1 

0.6728 

.2 

0.7136 

.2 

0.6993 

.2 

0.6856 

.2 

0.6724 

.3 

0.7132 

.3 

0.6990 

.3 

0.6853 

.3 

0.6721 

.4 

0.7128 

.4 

0.6986 

.4 

0.6849 

.4 

0.6718 

.5 

0.7125 

.5 

0.6983 

.5 

0.6846 

.5 

0.6715 

.6 

0.7121 

.6 

0.6979 

.6 

0.6843 

.6 

0.6711 

.7 

0.7117 

.7 

0.6976 

.7 

0.6839 

.7 

0.6708 

.8 

0.7114 

.8 

0.6972 

.8 

0.6836 

.8 

0.6705 

.9 

0.7110 

.9 

0.6969 

.9 

0.6833 

.9 

0.6702 

67.0 

0.7107 

71.0 

0.6965 

75.0 

0.6829 

79.0 

0.6699 

.1 

0.7103 

.1 

0.6962 

.1 

0.6826 

.1 

0.6695 

.2 

0.7099 

.2 

0.6958 

.2 

0.6823 

.2 

0.6692 

.3 

0.7096 

.3 

0.6955 

.3 

0.6819 

.3 

0.6689 

.4 

0.7092 

.4 

0.6951 

.4 

0.6816 

.4 

0.6686 

.5 

0.7089 

.5 

0.6948 

.5 

0.6813 

.5 

0.6683 

.6 

0.7085 

.6 

0.6944 

.6 

0.6809 

.6 

0.6679 

.7 

0.7081 

.7 

0.6941 

.7 

0.6806 

.7 

0.6676 

.8 

0.7078 

.8 

0.6938 

.8 

0.6803 

.8 

0.6673 

.9 

0.7074 

.9 

0.6934 

.9 

0.6799 

.9 

0.6670 

168.0 

0.7071 

72.0 

0.6931 

76.0 

0.6796 

80.0 

0.6667 

0.7067 

.1 

0.6927 

.1 

0.6793 

'.2 

0.7064 

.2 

0.6924 

.2 

0.6790 

.3 

0.7060 

.3 

0.6920 

.3 

0.6786 

.4 

0.7056 

.4 

0.6917 

.4 

0.6783 

.5 

0.7053 

.5 

0.6914 

.5 

0.6780 

.6 

0.7049 

.6 

0.6910 

.6 

0.6776 

.7 

0.7046 

.7 

0.6907 

.7 

0.6773 

.8 

0.7042 

.8 

0.6903 

.8 

0.6770 

.9 

0.7039 

.9 

0.6900 

.9 

0.6767 

69.0 

0.7035 

73.0 

0.6897 

77.0 

0.6763 

.1 

0.7032 

.1 

0.6893 

.1 

0.6760 

.2 

0.7028 

.2 

0.6890 

.2 

0.6757 

.3 

0.7025 

.3 

0.6886 

.3 

0.6753 

.4 

0.7021 

.4 

0.6883 

.4 

0.6750 

.5 

0.7018 

.5 

0.6880 

.5 

0.6747 

.6 

0.7014 

.6 

0.6876 

.6 

0.6744 

.7 

0.7011 

.7 

0.6873 

.7 

0.6740 

.8 

0.7007 

.8 

0.6869 

.8 

0.6737 

.9 

0.7004 

.9 

0.6866 

.9 

0.6734 

608 


THE    MODERN    ASPHALT    PAVEMENT. 


FACTORS. 
METRIC  TO  U.  S.  .STANDARD  WEIGHT,  MEASURES,  ETC. 


1  Milligram 
1  Gram 
1  Kilo 

1  Grain 

1  Ounce  (Av'd.) 

1  Pound 

1  Centimeter 
1  Meter 
1  Meter 
1  Kilometer 

1  Inch 
1  Foot 
1  Yard 
1  Statute  mile 

1  Liter 
1  Liter 
1  Cubic  meter 

1  Quart 
1  Gallon 
1  Gallon 

1  Square  centimeter  ' 

1  Square  meter 
1  Square  meter 
1  Square  kilometer 

1  Square  inch 
1  Square  foot 
1  Square  yard 
1  Square  mile  ' 

1  Cubic  centimeter  ' 

1  Cubic  meter  < 

1  Cubic  meter  < 

1  Cubic  inch  < 

1  Cubic  foot  i 

1  Cubic  yard  < 

1  Kilogram  per  square  centimeter  -• 
1  Kilogram  per  square  meter  < 
1  Kilogram  per  cubic  meter  • 

1  Pound  per  square  inch  « 

1  Pound  per  square  foot  < 

1  Pound  per  cubic  foot  • 

1  Gram  per  100  cubic  centimeter  > 


=        .01543  Grain 

=        .03572  Ounce  (Av'd.) 

=     2.205      Pounds  (Av'd.) 

=  64.799      Milligrams 
=   28.3495    Grams 
=       .4536    Kilogram 

=       .3937  Inch 

=  3.281  Feet 

=  1.0936  Yards 

=  .6214  Statute  mile 

=  2.540  Centimeters 

=       .3048  Meter 

=       .9144  Meter 

=  1.6093  Kilometers 

=  1.0567  Quarts 
=  .2647  Gallon 
=  264.1705  Gallons 

=       .9464    Liter 

=     3.7854    Liters 

=       .00379  Cubic  meter 

=»  .1550  Square  inch 

=  10.764  Square  Feet 

=  1.196  Yards 

=  .3861  Mile 

=  6.4516  Square  centimetew 

=       .0929  Square  meter 

=       .8361  Square  meter 

=  2.59  Square  kilometer* 

=  .06102  Cubic  inch 
=  35.31445  Cubic  feet 
=  1.3079  Cubic  yards 

=  16.3872    Cubic  centimeters 
=       .02832  Cubic  meter 
=       .76456  Cubic  meter 

14.2234    Pounds  per  square  inch 
.20482  Pound  per  square  foot 
.06243  Pound  per  cubic  foot 

.07031  Kilo  per  square  centimeter 
4.8824    Kilos  per  square  meter 
16.0184    Kilos  per  cubic  meter 

.624      Pound  per  cubic  foot 


APPENDIX. 


609 


TEMPERATURES  CENTIGRADE  AND  FAHRENHEIT. 


c. 

F. 

o 

C. 

0 

F. 

0 

C. 

0 

F. 

0 

C. 

0 

F. 

o 

C. 

o 

F. 

o 

-29 

-20.2 

-1-39 

+  102.2 

4-107 

+224.6 

+  175 

+347.0 

+243 

+469.4 

28 

18.4 

40 

104.0 

108 

226.4 

176 

348.8 

244 

471.2 

27 

16.6 

41 

105.8 

109 

228.2 

177 

350.6 

245 

473.0 

26 

14.8 

42 

107.6 

110 

230.0 

178 

352.4 

246 

474.8 

25 

13.0 

43 

109.4 

111 

231.8 

179 

354.2 

247 

476.6 

24 

11.2 

44 

111.2 

112 

233.6 

180 

356.0 

248 

478.4 

23 

9.4 

45 

113.0 

113 

235.4 

181 

357.8 

249 

480  2 

22 

7.6 

46 

114.8 

114 

237.2 

182 

359.6 

250 

482.0 

21 

5.8 

47 

116.6 

115 

239.0 

183 

361.4 

251 

483.8 

20 

4.0 

48 

118.4 

116 

240.8 

184 

363.2 

252 

485.6 

19 

2.2 

49 

120.2 

117 

242.6 

185 

365.0 

253 

487.4 

18 

0.4 

50 

122.0 

118 

244.4 

186 

366.8 

254 

489.2 

17 

+  1.4 

51 

123.8 

119 

246.2 

187 

368.6 

255 

491.0 

16 

3.2 

52 

125.6 

120 

248.0 

188 

370.4 

256 

492.8 

15 

5.0 

53 

127.4 

121 

249.8 

189 

372.2 

257 

494.6 

14 

6.8 

54 

129.2 

122 

251.6 

190 

374.0 

258 

496.4 

13 

8.6 

55 

131.0 

123 

253.4 

191 

375.8 

259 

498.2 

12 

10.4 

56 

132.8 

124 

255.2 

192 

377.6 

260 

500.0 

11 

12.2 

57 

134.6 

125 

257.0 

193 

379.4 

261 

501.8 

10 

14.0 

58 

136.4 

126 

258.8 

194 

381.2 

!  262 

503.6 

9 

15.8 

59 

138.2 

127 

260.6 

195 

383.0 

|  263 

505.4 

8 

17.6 

60 

140.0 

128 

262.4 

196 

384.8 

264 

507.2 

19.4 

61 

141.8 

129 

264.2 

197 

386.6 

265 

509.0 

21.2 

62 

143.6 

130 

266.0 

198 

388.4 

266 

510.8 

5 

23.0 

63 

145.4 

131 

267.8 

199 

390.2 

267 

512.6 

4 

24.8 

64 

147.2 

132 

269.6 

200 

392.0 

268 

514.4 

3 

26.6 

65 

149.0 

133 

271  .4 

201 

393.8 

269 

516.2 

2 

28.4 

66 

150.8 

134 

273.2 

202 

395.6 

270 

518.0 

1 

30.2 

67 

152.6 

135 

275.0 

203 

397.4 

271 

519.8 

0 

32.0 

68 

154.4 

136 

276.8 

204 

399.2 

272 

521.6 

+  1 

33.8 

69 

156.2 

137 

278.6 

205 

401.0 

273 

523.4 

2 

35.6 

70 

158.0 

138 

280.4 

206 

402.8 

274 

525.2 

3 

37.4 

71 

159.8 

139 

282.2 

207 

404.6 

275 

527.0 

4 

39.2 

72 

161.6 

140 

284.0 

208 

406.4 

276 

528.8 

5 

41.0 

73 

163.4 

141 

285.8 

209 

408.2 

277 

530.6 

6 

42.8 

74 

165.2 

142 

287.6 

210 

410.0 

278 

532.4 

7 

44.6 

75 

167.0 

143 

289.4 

211 

411.8 

279 

534.2 

8 

46.4 

76 

168.8 

144 

291.2 

212 

413.6 

280 

536.0 

9 

48.2 

77 

170.6 

145 

293.0 

213 

415.4 

281 

537  8 

10 

50.0 

78 

172.4 

146 

294.8 

214 

417.2 

282 

539.6 

11 

51.8 

79 

174.2 

147 

296.6 

215 

419.0 

283 

541.4 

12 

53.6 

80 

176.0 

148 

298.4 

216 

420.8 

284 

543.2 

13 

55.4 

81 

177  8 

149 

300.2 

217 

422.6 

285 

545.0 

14 

57.2 

82 

179.6 

150 

302.0 

218 

424.4 

286 

546.8 

15 

59.0 

83 

181.4 

151 

303.8 

219 

426.2 

287 

548.6 

L6 

60.8 

84 

183.2 

152 

305.6 

220 

428.0 

288 

550.4 

17 

62.6 

85 

185.0 

153 

307.4 

221 

429.8 

289 

552.2 

18 

64.4 

86 

186.8 

154 

309.2 

222 

431.6 

290 

554.0 

19 

66.2 

87 

188.6 

155 

311.0 

223 

433.4 

300 

572.0 

20 

68.0 

88 

190.4 

156 

312.8 

224 

435.2 

310 

590.0 

21 

69.8 

89 

192.2 

157 

314.6 

225 

437.0 

320 

608.0 

22 

71.6 

90 

194.0 

158 

316.4 

226 

438.8 

330 

626.0 

23 

73.4 

91 

195.8 

159 

318.2 

227 

440.6 

340 

644.0 

24 

75.2 

92 

197.6 

160 

320.0 

228 

442.4 

350 

662.0 

25 

77.0 

93 

199.4 

161 

321.8 

229 

444.2 

360 

680.0 

26 

78.8 

94 

201.2 

162 

323.6 

230 

446.0 

370 

698.0 

27 

80.6 

95 

203.0 

163 

325.4 

231 

447.8 

380 

716.0 

28 

82.4 

96 

204.8 

164 

327.2 

232 

449.6 

390 

734.0 

29 

84.2 

97 

206.6 

165 

329.0 

233 

451.4 

400 

752.0 

30 

86.0 

98 

208  4 

166 

330.8 

234 

453.2 

410 

770.0 

31 

87.8 

99 

210.2 

167 

332.6 

235 

455.0 

420 

788.0 

32 

89.6 

100 

212.0 

168 

334.4 

236 

456  8 

430 

806.0 

33 

91.4 

101 

213  8 

169 

336.2 

237 

458.6 

440 

824.0 

34 

93.2 

102 

215.6 

170 

338.0 

238 

460.4 

450 

842.0 

35 

95.0 

103 

217  A 

171 

339.8 

239 

462.2 

460 

860.0 

36 

96.8 

104 

219.2 

172 

341.6 

240 

464.0 

470 

878.0 

37 

98.6 

105 

221.0 

173 

343.4 

241 

465.8 

480 

896.0 

38 

100.4 

106 

222.4 

174 

345.2 

242 

467.6 

490 

914.0 

500 

932.0 

CONCLUSION. 

In  closing  these  pages  the  author  may  say  that  the  statements 
which  have  been  made  are  all  founded  on  his  own  experience,  and 
that  the  data  which  have  been  presented  are  the  result  of  ex- 
aminations and  investigations  carried  on  in  his  own  laboratory, 
except  where  it  is  stated  to  the  contrary.  The  conclusions  which 
have  been  drawn,  of  course,  involve  his  judgment  as  well  as  his 
experience,  but  they  have  been  based  on  practical  results  rather 
than  upon  theories,  as  the  latter  often  do  not  lead  to  success  in  the 
construction  of  asphalt  surfaces  or  to  a  satisfactory  explanation 
of  defective  work. 

An  attempt  has  been  made  to  gather  together  such  information 
as  is  available  in  regard  to  the  asphalt-paving  industry  and  asphalt 
pavements  in  general,  in  a  form  which  will  appeal  to  and  be  under- 
stood by  the  practical  man,  the  engineer,  the  asphalt  expert  and, 
finally,  in  certain  chapters,  to  the  citizen  at  large.  If  the  result 
proves  in  any  way  successful  and  the  character  of  the  asphalt 
pavements  which  are  constructed  in  the  future  are  in  any  way 
improved  thereby,  it  will  be  a  sufficient  reward  for  the  labor  involved 
in  bringing  out  this  book. 

610 


INDEX. 


Acetone,  591 
Aggregate,  mineral,  30 

See  also  Mineral  aggregate 
Albertite,  217 

composition  of,  218,  219 
Alcatraz  asphalt,  200,  245 
Analysis,  methods  of,  519 
Appendix,  599 
Ash,  determination  of,  542 

Asphalt,  action  of  water  on,  in  laboratory,  285,  461,  462 
Alcatraz,  200,  245 

x  associated  with  mineral  matter,  153 
Bermudez,  178 

crude,  extremes  in  composition  of,  183 
hardening  of,  181 
refined,  184 

bitumen,  ultimate  composition,  188 
composition  of,  186 
extremes  in  composition  of,  187 
relative  per  cent  of  flow  of  different  cargoes,  184 
California,  200 

La  Patera,  200 
More  Ranch,  202 
other  deposits,  206 
Standard,  203 
See  also  Residual  pitches 
Cuban,  192 
"D"  grade,  physical  characteristics  and  proximate  composition  of, 

258-260 
specifications  for,  263 

611 


612  INDEX. 

Asphalt,  defects  in  asphalt  surfaces  due  to  inferiority  of,  477 
definition  of,  150 
Maracaibo,  190,  191 
Mexico,  194 

Chapapote,  198 
Chijol,  196 

Tamesi  river,  194-196 
Tuxpan,  198 

physical  properties,  determination  of,  533 
rock,  Continental,  252 
specific  heat  of,  436 
Texas,  240 

Uvalde  County,  240 
Trinidad  lake,  156 

bitumen,  ultimate  composition  of,  169 
composition  of  crude,  160,  163 

refined,  163,  164 
constitution  of  crude,  160 
extremes  in  composition  of  refined,  165 
the  bitumen  of,  168 

mineral  matter  in,  161,  165 
land,  171 

average  composition  of  crude,  174 
composition  of  refined,  176 
extremes  in  composition  of,  177 
use  in  asphalt  surfaces,  lack  of  intelligence  in,  477 
Warren's  characterization,  150 
Asphalts,  Continental  rock,  252 

differentiation  of,  among  themselves,  152 

hard,  examination  of,  530 

individual,  156 

loss  on  heating,  determination  of,  534,  554,  555 

native,  comparison  of  their  relative  merits  for  paving  purposes, 

278 
physical  properties  of,  533 

and  proximate  composition  of  more  important, 

148,  149 

refined,  examination  of,  531 
the,  147 
Alphalt-block,  389 

See  also  Block,  asphalt-paving. 

Asphalt  cement,  amount  of  residuum  necessary  in  making,  300,  308 
Bermudez,  effect  of  water  on,  466 
California,  effect  of  water  on,  466 


INDEX.  613 

Asphalt  cement,  changes  in  consistency  of,  on  maintaining  in  a  melted  con- 
dition, 571 
change  in  consistency  of,  with  variation  of  temperature,  309, 

564 
characteristics  at  different  temperatures,  when  made  with 

light  and  heavy  flux,  310 
comparison  of  consistency  of,  when  made  with  different 

fluxes,  301 

consistency,  determination  of,  558 
determination  of  composition  of,  569,  571 

susceptibility  to  changes  in  temperature  of, 

564 

ductility,  see  Ductility 
examination  of,  558 
gilsonite,  211,  280,  306 
ductility,  211 

grahamite,  ductility  of,  213 
pneumatic  lift  for,  404 
the  character  of  various,  296 

preparation  of,  293 
Asphalt  cements,  composition  of  those  made  with  paraffine  and  asphaltic 

fluxes  and  various  asphalts,  297,  308 
containing  blown  oil,  307 
effect  of  filler  ou  ductility,  373 
made  from  residual  pitches,  307 

with  asphaltic  flux,  composition  of,  297,  303 
natural  malthas,  304 
paraffine  residuum,  296 
physical  properties  of,  308 
stability  at  high  temperature,  301,  571 
Asphalt  pavement,  merits  of,  455 
Asphalt  pavements,  action  of  water  on,  460 

on  the  street,  461,  495 
illuminating-gas  on,  491-494 
causes  of  the  defects  in  and  deterioration  of,  471 
cost  of,  457 

maintenance  of,  458 
grades  suitable  for,  450 
maintenance  of,  445,  458,  504 
specifications  for,  see  Specifications 
See  also  Asphalt  surfaces 

Asphalt  surfaces,  absorption  of  water  by,  465,  468 
contraction  of,  425 
cracking  of,  480 


614  INDEX. 

Asphalt  surfaces,  defects  in,  471 

See  also  Defects 
deterioration  of,  471 

due  to  environment,  499-502 

expansion  of  cement  in  foundation, 

499 

natural  wear,  502 
neglect  of  maintenance,  502 
disintegration  of,  490 

due  to,  490 

action  of  illuminating-gas,  491-494 
inferior  mixture,  491 
poor  workmanship,  496 
water  action,  461,  495 
displacement  of,  498 
effect  of  climate  on,  484 

radiation,  expansion,   contraction,  and  resistance  to  im- 
pact, 425 
scaling  of,  497 
strength  of,  485-490 
See  also  Surface  mixture 
Aephaltenes,  121,  122 
Asphaltic  or  bituminous  concrete,  348,  376 

binder,  25,  388 
examination  of,  576 

See  also  Concrete,  asphaltic  or  bituminous 
limestones,  221 

American,  characteristics  of,  238 
Continental,  252 
Oklahoma,  232,  238 
Texas,  240 
Utah,  248 
sands,  221 

bitumen  impregnating,  224,  228 
California,  243 

Carpinteria,  246 
San  Luis  Obispo,  244 
Santa  Barbara,  245 
Santa  Cruz,  243 
Kentucky,  221 

importance  of,  229 
Oklahoma,  230-239 
Texas,  240 
Utah,  248 


INDEX.  615 

Balance,  Chaslyn,  574 

sand,  523 

Base  or  foundation,  see  Foundation 
Beaume  degrees  and  specific  gravity,  604 
Bermudez  asphalt,  see  Asphalt 

asphalt  cement,  effect  of  water  on,  466 
Binder,  analysis  of  close  or  compact,  26 
asphaltic  concrete,  25,  388 
consistency  of  asphalt  cement  in  use  in,  23,  439 
course,  21 

placing  on  street,  413 
specifications  for  close  or  compact,  439 

open,  438 

of  Kansas  City,  Mo.,  599 

Bitumen,  amount  of,  which  sands  and  mineral  aggregates  will  carry,  361 
determination  of,  in  surface  mixtures,  571 
insoluble  in  carbon  tetrachloride,  124 
in  surface  mixtures  before  1896,  319 
litho-carbon,  241 

naphtha  soluble,  determination  of,  542 
pure,  preparation  of,  547,  548 
soluble  in  carbon  disulphide,  123 

tetrachloride,  546 
specific  heat  of,  426 

total,  determination  of,  in  asphalts,  540 
Bitumens,  identification  of,  586 

native,  characterization  and  classification  of,  110 
differentiation  of,  1 15 
in  use  in  the  paving  industry,  115 
physical  properties  of,  115 
solid,  chemical  characteristics  of,  121 
color  of  powder  or  streak,  119 
fixed  carbon  in,  122,  125 
flowing  of,  120 
fracture  of,  120 
hardness  of,  120 
lustre  of,  119 
odor  of,  120 
softening  of,  120 
specific  gravity  of,  117 
structure  of,  119 
solid,  147 

native,  not  asphalt,  208 

the  product  of  condensation  of  heavy  oils,  272 


616  INDEX. 

Bituminous  macadam,  see  Concrete,  asphaltic  or  bituminous 
Block,  asphalt-paving,  389 

analysis  of  various  manufacturers',  393 
method  of,  576 

components  entering  into  composition  of,  390 
Blown  oil  in  asphalt  cement,  307 

Bulletin  No.  1,  Barber  Asphalt  Paving  Company,  March,  1896,  322 
Byerlyte,  273 

California  asphalt,  see  Asphalt 

asphaltic  sands  in,  243-246 
See  also  Asphaltic  sands 

California  oil  asphalt  cement,  effect  of  water  on,  466 
Camber,  suitable  for  asphalt  streets,  451 
Carbenes,  122,  124,  546 
Carbon  disulphide,  590 

bitumen  soluble  in,  123 
fixed,  122,  125 

determination  of,  549 
tetrachloride,  590 

bitumen  insoluble  in,  124,  546 
Cement,  asphalt,  examination  of,  558 
curb,  446 

expansion  of,  in  foundation,  499 
hydraulic,  character  of,  13 
Centrifugal  method  for  examination  of  asphaltic  or  bituminous  concrete  and 

asphalt  paving  blocks,  576 
surface  mixtures,  573 

Chicago,  surface  mixtures,  1898  and  1899,  produced  without  technical  super- 
vision, 337 
Chloroform,  589 

Clay  soils,  specifications  for  the  construction  of  asphalt  pavements  on,  448 
Climate,  effect  of,  on  asphalt  surfaces,  484 
Color  of  powder  or  streak  of  bitumen,  119 
Colorado,  bitumen  in,  246 
Conclusion,  610 
Concrete,  asphaltic  or  bituminous,  348,  375-388 

analysis  of,  380,  381,  383 
production  of,  386 

plant  for,  407 
specifications  for,  441 
See  also  Asphaltic  or  bituminous  concrete. 
coal  tar,  378,  379 

Evans'  pavement,  Washington,  D.  C.,  laid  in  1873,  375 


INDEX.  617 

Continental  asphaltic  limestones,  252 

Contraction  of  asphalt  surfaces,  425 

Cracking  of  asphalt  surfaces,  480 

Crown,  formulas  for,  for  streets  of  different  width,  452,  453 

suitable  for  asphalt  streets,  451 
Crusher  screenings,  12 
Cuban  asphalt,  see  Asphalt 
Curb,  cement,  446 
Cushion  coat,  19-21 
Cyclic  hydrocarbons,  103 

Cylinders,  table  for  determining  the  cubic  contents  of,  582 

surface  of,  584 

Defects  in  asphalt  surfaces,  causes  of,  471 

due  to  careless  workmanship,  477 
character  of  filler,  476 
improper  specifications,  472 
inferior  sand,  324,  327,  474 
inferiority  in  the  asphalt  or  lack  of  intelli- 
gence in  its  use,  477 
lack  of  lateral  support,  15,  473 
manner  in  which  they  are  manifested,  479 
Density,  determination  of,  in  surface  mixture?,  580 

See  also  Specific  gravity 
Deterioration  in  asphalt  surfaces,  causes  of,  471 

See  also  Asphalt  surfaces 
Determination  of  bitumen  in  surface  mixture,  571 

insoluble  in  carbon  tetrachloride,  546 
character  of  filler,  529 
composition  of  asphalt  cement,  569-571 
consistency  of  asphalt  cement,  559 
density  and  voids  in  surface  mixture,  580 
flash-point,  554 

insoluble  matter,  or  difference,  123 
loss  on  heating  asphalts,  or  fluxes,  534,  554 
mineral  matter  or  ash,  542 
naphtha  soluble  bitumen,  542 
paraffine  scale,  556-558 
physical  properties  of  asphalt,  533 
melting  or  flowing  points,  538 
sand  grading,  521,  526 
specific  gravity,  552 
viscosity,  554 
voids  in  sands  and  mineral  aggregates,  526 


618  INDEX. 

Determination  of  volume  weight  of  sand,  528 

water  absorption  by  surface  mixtures,  583 
See  also  Examination 
Dow,  A.  W.,  491,  495,  559 
Drainage,  4,  5 

of  clay  soils,  448 
Drum,  sand,  396,  401 

Ductility  of  asphalt  cement,  effect  of  filler  on,  373 
gilsonite  asphalt  cement,  211 
grahamite  asphalt  cement,  213 
Dust,  see  Filler 

Ebano  asphalt,  see  Residual  pitch 
Elutriation  test,  see  Filler 
Examination  of  asphalt  blocks,  576 
cement,  558 
asphaltic  concrete,  576 
hard  asphalts,  530 
refined  asphalt,  531 
surface  mixture,  571 

by  centrifugal  method,  573 
stone,  gravel,  slag,  etc.,  519 
See  also  Determination  of 

Expansion,  coefficient  of,  of  materials  in  use  in  asphalt  surface  mixture,  481 
of  asphalt  surfaces,  427 

coefficient  of,  481,  483 
Ether,  591 

Filler,  87 

defects  in  asphalt  surfaces  due  to  inferiority  of,  476 

determination  and  character  of,  529 

of  character  of,  by  elutriation  method,  92,  529 

effect  of,  on  ductility  of  asphalt  cement,  373 

method  of  examining,  92,  529 

number  of  particles  and  square  feet  of  surface  in  one  pound  of  New 
York  filler,  359 

portion  of  200-mesh  material  acting  as,  346,  348,  349,  364 

role  played  by,  in  preventing  water  action,  373 

size  of  particles  in,  94 

volume  weight  of,  94 
Fixed  carbon,  see  Carbon 
Flash-point,  determination  of,  554 

Flint,  crushed,  weight  per  cubic  foot  and  voids  compared  with  those  in 
sand,  83 


INDEX.  619 

Flow-test,  567-569 

Flowing  of  native  solid  bitumens,  115 
Flux,  amount  of,  necessary  in  making  asphalt  cement,  300 
asphaltic,  136 

comparison  of  asphalt  cements  made  with,  297 
Beaumont,  Texas,  141 

or  similar,  141 

specifications  for,  142 
California,  "G"  grade,  136-139 

defects  in,  139 
specifications  for,  139 
comparison  of,  consistency  of  asphalt  cements  at  different  temperatures 

when  made  with  different  fluxes,  301 
light  and  heavy,   characteristics  of  asphalt   cements  made  with,   at 

different  temperatures,  311 

paraffine,  composition  of  asphalt  cements  made  with,  297 
Pittsburg,  272 

Texas,  Beaumont,  and  similar,  141 
Ventura,  272 
See  also  Residuum 
Fluxes,  127 

examination  of,  550 

loss  on  heating,  determination  of,  534,  554,  555 
Formulas  for  crowns  of  streets  of  different  width,  452,  453 
Foundation,  or  base,  3 

bituminous,  6 

expansion  of  cement  in,  499 
granite  block,  8 
hydraulic  concrete,  9 
old  brick  pavement,  8 
macadam,  7 
subsoil,  4 
Fracture  of  solid  native  bitumens,  120 

Gas,  illuminating,  action  on  asphalt  surfaces,  491-494 

composition  of,  493 
Gilsonite,  208 

asphalt  cement,  ductility  of,  210,  211.  280 

composition  of,  208 

in  use  in  the  paving  industry  211,  288 
Glance-pitch,  213 

composition  of,  215 

Grades  suitable  for  asphalt  pavements.  450 
Grading,  comparison  of  different  sands  having  the  same,  361 


620  INDEX. 

Grading,  extension  of,  when  containing  much  coarser  and  much  finer  parti- 
cles than  the  standard,  347 
of  sands,  84 

determination  of,  521-526 
in  various  cities,  with  and  without  filler,  362 
standard,  332,  342 
Grahamite,  192,  211 

asphalt  cement,  ductility  of,  2i3 
composition  of,  212,  214 
in  use  in  the  paving  industry,  213 
Oklahoma,  239 

Grains,  number  of,  in  one  gram  of  sand  of  uniform  diameter,  358 
Granite  blocks,  foundation,  7 
Gravel  in  conrcete  base,  9,  11,  437 
Gutters  for  asphalt  streets,  453 

Hardness  of  native  solid  bitumens,  120 

Heat,  absorption  and  radiation  of,  by  various  pavements,  425-427 

specific,  of  asphalt,  426 
Heaters,  sand,  396,  401 

surface,  for  use  in  repairs  to  asphalt  pavements,  507 
Heating,  asphalts  and  fluxes,  determination  of  loss  on,  534,  554 
Horses'  feet,  effect  of,  on  asphalt  pavement,  428 
Hydrocarbons,  chain,  98 

cyclic,  103 

unsaturated,  104 

derivatives,  108 

dicyclic,  105 

native,  98 

olefine,  102 

paraffine,  101 

polycyclic,  106 

polymethylene,  103,  106 

saturated,  99 

unsaturated,  102 
Hydrolene"B,"273 

Impact  tests  of  asphalt  surface  mixture,  287,  428 

method  of  making,  585 
Identification  of  bitumens,  586 
Indianapolis,  Ind.,  defective  surface  mixture,  337 
Inorganic  matter,  123 
Intermediate  course,  19 


INDEX.  621 

Kentucky  asphaltic  sands,  see  Asphaltic  sands 

bituminous  sands,  221-229 
Kettles,  see  Tanks 

Laboratory  equipment,  595 

Lateral  support,  defects  in  asphalt  surfaces  due  to,  15,  473 

Lift,  pneumatic,  for  asphalt  cement,  404 

Limestones,  asphaltic,  221 

American,  238 

Continental,  252 

Oklahoma,  232-238 
Litho-carbon  bitumen,  241 
London,  England,  surface  mixture,  328 
Lustre  of  native  solid  bitumens,  119 

Macadam  as  a  foundation,  7 

bituminous,  see  Concrete,  asphaltic  or  bituminous 
Machinery  for  producing  asphalt  surface  mixture,  400 
Maintenance,  cost  of,  of  asphalt  pavements,  458,  504 
due  to  natural  wear,  502 
of  asphalt  pavements,  445,  458,  504 
Maltha  as  a  flux,  304 
Malthas,  127 

natural,  asphalt  cements  made  with,  304 
Malthenes,  121,  124 

determination  of  character  of,  544 
in  asphalts,  542 
Manjak,  213 

composition  of,  216 
Maracaibo  asphalt,  see  Asphalt 

Materials,  instructions  for  collecting  samples  of,  509 
Measures  and  weights,  table  for  converting  metric  to  U.  S.  standards,  608 
Melting-tanks,  398,  404 
Merits  of  asphalt  pavement,  455 

asphalts  for  paving  purposes,  opinion  of  Western  chemist  on,  281 
various  asphalts  for  paving  purposes,  276 
Methods  of  analysis,  519 
Mexico,  asphalt,  see  Asphalt 
Mineral  aggregate,  30 

1892-1899,  317-319 

amount  of  bitumen  which  it  will  carry,  351 
extension  of  grading  of,  when  containing  much  coarser 
and  much  finer  particles  than  the  standard,  347 


622  INDEX. 

Mineral  aggregate,  voids  in,  method  of  determining,  526 

See  also  Sand 

matter  associated  with  asphalt,  153 
determination  of,  542 
in  Trinidad  lake  asphalt,  165 

Mixer  for  making  surface  mixture  and  binder,  406 
Mixture,  surface,  see  Surface  mixture 

Naphthas,  592 

Naphtha  soluble  bitumen,  determination  of,  542 

New  York  defective  surface  mixtures,  325,  326,  338 

mixtures  produced  in,  with  inferior  sand  grading,  338,  475 

Odor  of  native  solid  bitumens,  120 
Oils,  blown,  273 

in  asphalt  cements,  307 

Oklahoma,  asphaltic  limestones,  232,  234,  238 
sands,  230-239 

deposits  of  bitumen,  230 

grahamite,  239 

value  of  the  bituminous  deposits  of,  for  paving  purposes,  240 
Omaha  surface  mixtures,  322 
Oven  employed  in  author's  laboratory,  535-538 
Ozocerite,  217 

Paint-coat,  27 

specifications  for,  28 
Paraffine  scale,  determination  of,  556-558 

in  residuum,  134 

Particles,  size  of,  passed  by  sieves,  59 
Pat  paper  test,  352-356 

method  of  making,  514,  515 
Paving  industry,  bitumens  in  use  in,  115 
Penetration  machines,  559-567 

Bowen,  559 
Dow,  559 

New  York  Testing  Laboratory,  565 
Petrolenes,  121 

Petroleum,  classification  of,  112 
Petroleums,  127 
Pitch,  residual,  asphalt  cements  made  from,  307 

differentiation  of,  from  natural  asphalt,  276 
from  California  petroleum,  256 
Kansas  petroleum,  273 


INDEX.  623 

Pitch,  residual,  from  Mexican  petroleum,  270 

petroleum,  256 

Russian  petroleum,  270,  271 

Texas  petroleum,  266 

See  also  Residual  pitch 
Pittsburg  flux,  272 

Plant,  for  production  of  bituminous  concrete,  407 
Plants,  permanent,  400 

portable  and  semi-portable,  406 
types  of,  400 

Polymethylene  hydrocarbons,  103,  106 
Powder,  color  of,  119 
Pyro-bitumens,  111,  217 
Physical  properties  of  asphalt,  533 

Radiation  of  various  pavemente,  425-427 
Rakes,  proper  type  of,  417 
Raking  surface  mixture,  417-419 
Refining  of  solid  bitumens,  291 

tanks,  404 
Residual  pitch,  asphalt  cements  containing,  as  an  amendment,  307 

made  from,  306 
characteristics  of,  256-277 
from  Kansas  petroleum  (Sarco),  273 
Mexican  petroleum  (Ebano),  270 
Texas  petroleum,  266 
See  also  Pitch,  residual 
Repairs  to  asphalt  pavements,  cost  of,  in  Washington,  D.  C.,  458,  504 

use  of  surface  heaters  in  making,  507 
Residuum,  asphaltic,  asphalt  cements  made  with,  296 

characteristics  of  asphalt  cements  at  different  temperatures  when 

made  with  light  and  heavy,  311 
complete  solubility  of  asphalt  in,  299 
examination  of,  550 
parafiine,  character  of,  131-136 
petroleum,  131 
scale  in.  134 
specifications  for,  134 
suitability  for  use  as  a  flux,  296 
petroleum,  127 

California  asphaltic,  136 

character  of,  137 
specifications  for,  139 
Kansas,  135 


624  IND^X. 

Residuum,  shale  oil,  144 

Texas,  141 

specifications  for,  142 

See  also  Flux 
Rollers,  419,  420 

Samples,  instructions  for  collecting,  509 
Sampling,  methods  to  be  employed  in,  512 
Sand,  30 

100-  and  80-mesh,  role  played  in  preventing  water  action,  373 

See  also  Sand,  fine 

amount  of  bitumen  it  will  carry,  351 
average  per  cent  of  200-mesh  in,  from  various  cities,  364 
balance,  523 
bituminous,  California,  243 

Carpinteria,  246 
San  Luis  Obispo,  244 
Santa  Barbara,  245 
Santa  Cruz,  243 
classification  of,  32 
concrete,  11 

defects  in  asphalt  surfaces  due  to  inferior  grade,  474 
effect  of  200-mesh,  on  surface  mixture,  345 
fine,  defects  of,  in  surface  mixtures,  323,  324,  328,  332,  334,  338-342, 

344,  345 
grading,   extension  when  containing  much  coarser  and  much  finer 

particles  than  the  standard,  347 

grading,  in  different  cities,  with  and  without  filler,  362 
lack  of  sand  for  obtaining  standard,  339 
mixture  produced  in  New  York  City  with  improper,  337,  475 
grains,  shape  of,  56 

size  of,  59,  60 
heaters,  396,  401 
New  York,  weight  and  voids  in,  with  various  percentages  of  200-mesh 

dust,  82 
number  of  particles  in  one  pound  of  mineral  aggregate,  New  York,  1895 

and  1898,  359 

number  of  particles  in  one  gram  ol  grains  of  uniform  diameter,  358 
sharp  as  compared  with  round,  84 
square  feet  of  surface  of  one  pound,  New  York  mineral  aggregate,  1895 

and  1898,  359 
standard  grading,  332,  342 

for  light  traffic,  342 
voids  in,  72,  526 


INDEX.  625 

Sand,  volume  weight  of,  determination  of,  528 

weight  and  voids  in  New  York  sand  with  various  percentages  of  200- 
mesh  dust,  82 

See  also  Mineral  aggregate 
Sands,  alluvial,  39 

artificial,  52 

asphaltic,  221 

Kentucky,  221 

bitumen  impregnating,  224,  228 
importance  of,  229 

See  also  Asphaltic  sands 

bank  or  pit,  46 

comparison  of  different,  having  the  same  grading,  361 

composition  of,  53 

determination  of  the  grading  of,  521 

glacial,  51 

grading  of,  84 

determination  of,  521-526 

pounds  per  cubic  foot  and  voids  in  various,  78,  81 

lakeshore,  36 

of  different  composition  having  the  same  grading,  361 

purchase  of,  53 

quick,  48 

river,  39 

seabeach,  34 

sieves  for  sifting,  59 

sifting  of,  59 

specific  gravity  of,  363 

surface  of,  57 

voids,  see  Sands,  weight  per  cubic  foot 

volume  weight  of  hot,  per  cubic  foot,  82 

weight  per  cubic  foot  and  voids  in  the  average,  from  various  cities, 
with  filler  to  make  200-mesh  material  equal  to  15  per  cent,  365,  366 

weight  per  cubic  foot  and  voids  in  New  York  sand  with  and  without 
dust,  compared  with  the  same  grading  of  sands  from  other  cities,  363 

weight  per  cubic  foot  and  voids  of,  compared  with  those  in  crushed 
flint,  83 

weight  per  cubic  foot  of,  77 
Sandy  soils,  449 
Sarco,  see  Residual  pitch 
Scaling  of  asphalt  surfaces,  497 
Screenings,  crusher,  12 
Sieves,  manufacture  of,  61 

method  of  using,  522,  525 


626  INDEX. 

Sieves,  uniformity  of,  59 

for  mechanical  sifting,  524 
Sifting  of  sand,  59 

Softening  of  native  solid  bitumens,  120 
Soils,  clay,  4 

specifications  for  construction  of  asphalt  pavements  on,  448 
sandy,  449 
Solvents,  589 
Specific  gravity,  determination  of,  552 

of  native  solid  bitumens,  117 

oils  or  fluxes,  method  of  determining,  in  use  in  Chicago 

City  laboratory,  552 
sands,  363 

surface  mixtures,  367 
Specific  heat  of  asphalt,  426 
Specifications,  435 

clay  soils,  4,  448 

defects  in  asphalt  surfaces  due  to  improper,  472 

for  asphalt  pavements,  435 

Kansas  City,  Mo.,  599 
asphaltic  concrete,  441 
compact  or  close  binder,  439 
"D"  grade  asphalt,  263 
"G"  grade  California  flux,  139 
open  binder,  438 
paraffine  residuum,  134 
Texas  or  similar  oil,  142 
St.  Louis  surface  mixture,  327 
Standard  grading,  332,  342 
Stone  block  pavement  as  foundation,  6,  7 
Stone,  examination  of,  519 
Street,  construction  work  on,  413 
railroad  tracks,  16 
transportation  of  materials  to,  412 
Structure  of  native  solid  bitumens,  119 
Subsoil,  4 

Sulphuric  acid,  action  on  hydrocarbons,  102,  124 
Support,  lateral,  15,  473 
Surface  course,  placing  on  street,  415 

heaters,  use  of,  in  repairing  asphalt  pavements,  507 
mixture,  313 

Bermudez,  destruction  of,  by  water,  463 

effect  of  three  months'  action  by  water,  465 
capacity  for  absorbing  water,  369-372 


INDEX.  627 

Surface  mixture,  characteristics,  indicative  of  the  properties  of,  old  and  new, 

367 
defects  in,  471 

due  to  inferiority  of  asphalt,  477 
density  of,  367 
determination  of  bitumen  in,  571 

density  and  voids  in,  580 
examination  of,  571 

by  centrifugal  method,  573 
impact  tests  of,  287,  428 

materials  in  use  in,  coefficient  of  expansion  of,  481 
on  rule  of  thumb  basis,  336 
points  for  consideration  in  a  standard,  332 
process  of  combining  the  constituents  into,  395 
raking  of,  417-419 
sampling  of,  514 
standard,  332,  342 

why  it  is  satisfactory,  371 
Trinidad  lake  asphalt,  effect  of  three  months'  action  on,  by 

water,  465 

See  also  Asphalt  surfaces 

Surface  mixtures,  action  of  water  on,  on  the  street,  461 
average  composition  before  1894,  314 

in  1897,  321 
Barber  Asphalt  Paving  Company,   1896-1899  and  1904, 

329-331 

bitupen  in,  before  1889-1899,  319,  320 
Chicago,    1898,    1899,   produced  without  technical  super- 
vision, 337 

coarser  than  standard,  339 
composition  of,  before  1894,  314 
defective,  Indianapolis,  Ind.,  337 
Toronto,  Canada,  337 
Utica,  N.  Y.,  337 
effect  of  200-mesh  sand  on,  345 
grading  of  sand  in,  before  1894,  316 
London,  England,  1896,  328 
made  with  fine  sand,  323,  324,  328,  332,  334,  337,  339-342, 

344,  345 

method  of  making  impact  tests,  585 
mushy,  349 

New  York,  defective,  1895,  325,  326,  338 
Omaha,   average   bitumen  in  good,   medium,   and  badly 
cracked  surfaces,  322 


628  INDEX. 

Surface  mixtures,  produced  in  New  York  City  in  1904  without  proper  super- 
vision of  sand  grading,  338,  475 
without  technical  supervision  in  Chicago  in  1898 

and  1899,  337 

St.  Louis,  1892  and  1893,  327 
standard  grading  for  light  traffic,  342 
Washington,  D.  C.,  1896,  327 
water  absorption  of,  583 


Tanks,  melting,  398,  404 

steam  melting,  404 

Technology  of  the  paving  industry,  291 
Temperature,  changes  in  consistency  of  asphalt  cement  with  variations  of, 

309,  564 

conversion  of  Centigrade  to  Fahrenheit  readings,  609 
different,  characterization  of  asphalt  cement  when  made  with 

light  and  heavy  fluxes,  at,  311 
high,  stability  of  asphalt  cements  at,  301,  571 
proper,  for  surface  mixture,  415,  416 
susceptibility  of  asphalt  cement  to  changes  in,  564 
Test,  pat  paper,  see  Pat  paper  test 
Texas,  asphaltic  limestones,  240 

sands,  240 

asphalts,  see  Asphalts 
Tools  for  use  on  street,  422 

Toronto,  Canada,  defective  surface  mixture,  337 
Traffic,  484 

and  lack  of  it,  effect  on  asphalt  surfaces,  484 
en  asphalt  pavements  in  New  York  City,  457 
Transportation  of  materials  to  the  street,  412 
Trinidad  asphalt,  see  Asphalt 
Turpentine,  oil  of,  590 

Utah,  asphaltic  sands,  see  Asphaltic  sands 

bituminous  sands  and  limestones,  248 

native  bitumens  of,  247 

See  also  Gilsonite,  Wurztilite,  and  Ozocerite 
Utica,  N.  Y.,  defective  surface  mixture,  337 

Ventura  flux,  272 
Vibration  of  rails,  16 
Viscosity,  determination  of,  554 


INDEX.  629 

Voids,  as  affected  by  size  and  shape  of  particles  and  by  their  uniformity,  77 
determination  of,  in  sand,  75 

surface  mixture,  580 
in  mineral  aggregates,  determination  of,  626 

sand,  72 
Volume  weight  of  filler,  94 

sand,  determination  of,  528 
sands,  hot,  per  cubic  foot,  82 
Washington,  D.  C.,  cost  of  repairs  to  asphalt  pavements  in,  458,  505 

surface  mixture,  327 
Water  absorption,  capacity  of  surface  mixture  for,  369,  372 

cause  of  action  of,  on  asphalt  under  certain  circumstances, 

467 
by  Trinidad  and  Bermudez  surface  mixtures,  pounds  per 

square  yard,  465 
of  surface  mixtures,  583 
action  of,  on  asphalt  pavements,  460 

in  the  laboratory,  285,  461,  462 
surfaces,  495 
actual  results  of  action  of,  on  asphalt  surface  mixtures  on  the  street, 

461 
comparison  of  action  of,  on  surface  mixtures  in  the  laboratory  and  on 

the  street,  462,  466 
effect  on  Bermudez  asphalt  cement,  466 

California  oil  asphalt  cements,  466 

relative  absorption  of,  by  coarse  and  fine  asphalt  surface  mixtures,  468 
Wax  tailings,  143-145 

Weights  and  measures,  table  for  converting  metric  to  U.  S.  standards,  608 
Whipple  &  Jackson,  asphalts,  action  of  water  on,  461 
Work,  control  of,  509 

inspection  of,  509 
Workmanship,  careless,  defects  in  asphalt  surfaces  due  to,  477 

poor,  disintegration  of  asphalt  surfaces,  due  to,  496 
Wurtzilite,  218 

composition  of,  220 


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